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1 Chapter 2Figure 2.1 Schematic of solar fuel feedstocks (CO₂, H₂O, and solar energy) and production path on‐site and/or transported to the solar refinery [4].Figure 2.2 Schematic diagrams of (a) natural photosynthesis and (b) artificial photosynthesis based on molecular systems. Source: Liu et al. [9].Figure 2.3 (a) Traditional catalytic processeson the surface of catalysts. (b) Classic photocatalytic paths over photocatalysts.Figure 2.4 A band‐gap diagram showing the different sizes of band gaps for conductors, semiconductors, and insulators.Figure 2.5 Proposed mechanism of photocatalytic reactions on semiconductor photocatalysts. Source: Ma et al. [16].Figure 2.6 A schematic illustration of the energy correlation between semiconductor catalysts and redox couples in water. CB and VB denote a conduction band and a valence band, respectively. Source: Tu et al. [20].Figure 2.7 (a) Yields of the products produced during the photocatalytic reduction of CO₂ with H₂O and photoluminescence of various Ti/FSM‐16 photocatalysts. (b) Product distribution of CO₂ photoreduction over 1‐TiO₂, 2–10 wt% imp‐TiO₂/Y‐zeolite, 3–1.0 wt% imp‐TiO₂/Y‐zeolite, 4‐ex‐TiO₂/Y‐zeolite, and 5‐Pt‐loaded ex‐TiO₂/Y‐zeolite. (c) Schematic mechanisms of the photocatalytic CO₂ reduction with H₂O on TiO₂. Source: (a) Ikeuea et al. [23]; (b) Anpo et al. [22]; (c) From Anpo et al. [21]. © 1995 Elsevier.Figure 2.8 Schematic cycle for the photosensitized reduction of CO₂ to CH₄. Source: Maidan and Willner [25].Figure 2.9 (a) Calculated band structures and total density of states of BMO‐OVs. Absorptive formats of CO₂ on BMO‐OVs (b) and BMO (c). CO₂ reduction pathways on BMO‐OVs (d) and BMO (e). (f) The diagram of band positions. (g) CH₄ production and the TCEN value for CO₂ photoreduction over the BMO‐OVs and BMO during four hours visible‐light irradiation. (h) Typical time course of CO/CH₄ generated over BMO‐OVs. Source: Yang et al. [30].Figure 2.10 (a) Schematic illustration of the solar‐assisted production of methanol from CO₂ and water through a three‐enzyme cascade. (b) Methanol production as a function of time in multienzymatic systems. (c) Photoelectrochemical production of methanol by TPIEC under various applied potentials under visible‐light illumination. (d) Methanol production of the TPIEC system in various multienzymatic systems with an external voltage of 0.8 V. Source: Kuk et al. [41].Figure 2.11 (a) Mechanism for the reduction of CO₂ by photocatalysis under visible light with a Ru complex and an N‐Ta₂O₅ hybrid catalyst. (b) Turnover number for HCOOH formation from CO₂ over various molecular systems as a function of irradiation time. (c) Schematic mechanism of visible‐light‐driven photocatalytic CO₂ reduction over RuP/NS‐C₃N₄ hybrids. (d) Time courses of photocatalytic CO₂ reduction using RuP/NS‐C₃N₄‐PU0 and RuP/NS‐C₃N₄‐PU90 under visible light (λ > 400 nm). Source: (a) Suzuki et al. [55]; (b) Sato et al. [55]; (c) Tsounis et al. [56]; (d) Tsounis et al. [56].Figure 2.12 (a) Scheme of the photocatalytic CO₂ reduction over CdS/(Cu–Na_xH_2−xTi₃O₇) irradiated by light. (b) Gas evolution rates of C1–C3 hydrocarbons on CdS/(Cu–Na_xH_2−xTi₃O₇) as well as the specific surface area, where the Na/Ti ratios were 0.093 (low), 0.143 (medium), and 0.507 (high). (c–e) Mass spectra of the formed hydrocarbons (methane, ethane, and propane) with the labeling of ¹³C. (f) Proposed elementary reaction mechanisms of photocatalytic CO₂ conversion into hydrocarbons. Source: Park et al. [64].Figure 2.13 Structures of CN before (a) and after (b) doping with carbon chains. (c) Electrochemical impedance spectroscopy (EIS) Nyquist plots under irradiation condition. Inset: Periodic on/off photocurrent response under visible‐light irradiation. (d) Comparison of the photocatalytic CO₂ reduction rate of the samples with different amount of glycine, respectively. Source: Ren et al. [70].Figure 2.14 (a) Gas production under six hours visible‐light irradiation of pure Cu₂O and Cl‐doped Cu₂O samples. (b) Mass spectrum from the ¹⁸O‐labeling H₂O isotope experiments of Cu₂O–Cl‐4. (c) Time‐dependent product evolution over Cu₂O–Cl‐4 under visible‐light irradiation. (d) Stability test of Cu₂O–Cl‐4. (e) Proposed reaction pathways of CO₂RR to CO and CH₄ on Cl‐doped Cu₂O. Source: Yu et al. [83].

2 Chapter 3Figure 3.1 The light‐dependent reactions of photosynthesis produce protons and electrons used in the conversion of CO₂ to carbohydrates (CH₂O) and other organic compounds, while oxidation of these organic compounds (biomass, food, fuels) by respiration or combustion releases the stored solar energy to power the metabolism of non‐photosynthetic organisms and drive human technologies.Figure 3.2 Schematic membrane arrangement of enzymes involved in the light‐dependent reactions of oxygenic photosynthesis. Red arrows indicate the flow of electrons from the primary electron donor H₂O to the final electron acceptor NADP⁺ aided by photoexcitation in photosystems II and I. Electron flow is tied to proton translocation across the membrane. The proton gradient created by accumulation of protons in the interior of the membrane powers the synthesis of ATP.Figure 3.3 Selected types of chlorophyll molecules encountered in natural photosynthesis.Figure 3.4 (a) Side and top view of the light‐harvesting complex LH2 from the purple bacterium R. acidophila 10050 (PDB: 1KZU [24]), showing bacteriochlorophyll a pigments in green and carotenoids (rhodopin glucoside) in orange. (b) Rod structure of c‐phycocyanin from the phycobilisome light‐harvesting antenna of cyanobacterium T. vulcanus (PDB: 3O18 [25]). (c) Light‐harvesting complex II (LHCII) from pea (PDB: 2BHW [26]), showing Chl a pigments in dark green and Chl b in light green.Figure 3.5 Examples of synthetic approaches to multi‐chromophore arrays: (a) a nine‐porphyrin array unit comprising a central free‐base porphyrin core that acts as final acceptor and is surrounded by eight energy‐donating zinc porphyrins [43]. Source: Choi et al. [41]Figure 3.6 Simplified Z‐scheme of natural oxygenic photosynthesis, showing how two photons are used per electron flowing from the terminal donor (H₂O) to the terminal acceptor (NADP⁺) of the light‐dependent reactions.Figure 3.7 Photosystem II from T. vulcanus (PDB ID: 3WU2, a) and major redox‐active components within a PS‐II monomer involved in the main‐pathway electron transfer indicated with red arrows (b).Figure 3.8 The cycle of intermediate oxidation states of the oxygen‐evolving complex. Water is assumed to bind at the S₃ state of the cluster and upon reconstitution of the S₀ state. The S₄ state is a postulated but unobserved transient intermediate that decays spontaneously to S₀ with release of dioxygen.Figure 3.9 The Mn₄CaO₅ cluster and its protein pocket in the dark‐stable S₁ state as revealed by protein crystallography (PDB ID: 3WU2, a), and a scheme showing the commonly used labeling of the ions comprising the inorganic core.Figure 3.10 Proposed models for the inorganic core in the S₂ state of the OEC, with the first coordination sphere mostly omitted for clarity. The different magnetic topologies of the two valence isomers, as expressed through the pairwise exchange coupling constants J_ij (values shown in cm⁻¹; J < 0 is antiferromagnetic coupling), lead to different total spin states and g values for the corresponding EPR signals.Figure 3.11 The S₂ → S₃ transition according to Retegan et al. [191] and possible isovalent Mn(IV)₄ components of the S₃ state; the superscript “W” indicates binding of an additional water ligand.Figure 3.12 Two selected scenarios for the nature of the S₄ state and OO bond formation from the computational literature: (a) formation of a Mn1(IV)‐oxyl group in the S₄ state is followed by odd‐electron radical oxyl–oxo coupling [285], and (b) formation of a five‐coordinate high‐spin Mn4(V)‐oxo is followed by intramolecular nucleophilic coupling with concerted water binding [289]. Thick lines indicate direction of Jahn–Teller axes of Mn(III) ions.Figure 3.13 Reaction mechanism of RuBisCO proposed by Taylor and Andersson. Source: Taylor and Andersson [351].

3 Chapter 4Figure 4.1 Schematic illustration of photocatalytic hydrogen generation over a semiconductor photocatalyst [8].Figure 4.2 Band levels of various semiconductor photocatalysts. Source: Lu et al. [15].Figure 4.3 Schematic cells for rutile phase (a) and anatase phase (b) of TiO₂. Source: Thompson and Yates [16].Figure 4.4 Photocatalytic H₂ evolution of pure TiO₂, Degussa P25, and TiO₂ with different amounts of Zn. Source: Al‐Mayman et al. [25].Figure 4.5 Hydrogen evolution on the bare and metallic TiO₂ photocatalysts using the benchmark Degussa P25 TiO₂ and its bimetallic materials as the references. Source: Wang et al. [26].Figure 4.6 Photocatalytic hydrogen evolution on TiO₂‐supported Au–Pd nanoparticles using a range of alcohols. Source: Su et al. [27].Figure 4.7 Schematic representation of the band structure of pure and N‐doped anatase TiO₂. Note that the energies are not in scale. Source: Di Valentin et al. [32].Figure 4.8 The photocatalyst H₂ generation rate of 2.5 wt%‐Cu₂O/TiO₂ with different sacrificial reagents. Source: Li et al. [34].Figure 4.9 (a) The energy band structure of ZnO/ZnS heterojunction. (b) The graphic structure of ZnO‐dotted ZnS. Source: Wu et al. [37].Figure 4.10 Tri‐s‐triazine‐based structure of g‐C₃N₄. The C and N atoms are indicated by gray and blue balls [8].Figure 4.11 Photocatalytic H₂ production over the bulk C₃N₄, C₃N₄ NSs, and C₃N₄ NTs under visible‐light irradiation. Source: Zhu et al. [54].Figure 4.12 Graphic design of preparation of cobalt‐doped g‐C₃N₄. Source: Chen et al. [57].Figure 4.13 (a) EIS, (b) photocurrent response, and steady‐state (c) and transient (d) PL spectra of g‐C₃N4 and B‐doped g‐C₃N₄ samples. Source: Chen et al. [60].Figure 4.14 Schematic illustration of the charge transfer for the three types of heterojunctions [8].Figure 4.15 Graphic illustration of the proposed mechanism for cobalt oxide/C₃N₄ NT heterojunction for photocatalytic H₂ evolution. Source: Zhu et al. [61].Figure 4.16 Schematic diagram of the photocatalytic mechanism in WO₃/MCN. Source: Kailasam et al. [63].Figure 4.17 The average H₂ evolution rate of the SiC nanowires and modified SiC nanowires. Source: Hao et al. [66].Figure 4.18 Illustration of lanthanide upconversion nanoparticles (UCNPs).Figure 4.19 Illustrative diagrams of energy transfer among NYFG(15)/C₃N₄ NTs. Source: Zhu et al. [67].Figure 4.20 The proposed mechanism of the improved photocatalytic activity in the N‐CDs/CdS photocatalyst. Source: Shi et al. [69].Figure 4.21 Graphic diagram of the FeS₂–TiO₂ heterostructures under ultraviolet, visible, and NIR light irradiation for photocatalytic H₂ evolution. Source: Kuo et al. [71].Figure 4.22 (a) The UV–vis near‐infrared absorption spectrum. (b) Photocatalytic hydrogen evolution for amorphous TiO₂–x. Source: Jiang et al. [74]Figure 4.23 Methanol and its dissociative species underwent two‐electron oxidation in photocatalytic H₂ production process over Au–Pt alloyed TiO₂ nanocomposites. Source: Al‐Mayman et al. [25].

4 Chapter 5Figure 5.1 The schematic illustration of the features of H₂ production by PV + EC, PEC, and PC in the five aspects of cost, STH efficiency, technology readiness, H₂/O₂ separation, and catalyst stability.Figure 5.2 The schematic illustration of three steps in PEC water splitting process. Source: From Wang and Wang [7]. © 2018 Elsevier.Figure 5.3 The illustration of semiconductor–electrolyte interface and the corresponding band bending. (a, b) The scheme and energy level of semiconductor and electrolyte in vacuum. The electrons are uniformly distributed around the core of atoms (blue dot). (c, d) The schematic illustration of electron distribution and the energy band bending when SEI is built. The electrons (red dot) are accumulated at the SEI interface. (e, f) The schematic illustration of electron–hole separation and transfer under illumination.Figure 5.4 (a) The oxygen vacancy concentration change by adjusting the treatment duration in N₂. (b) The volcano relationship between photocurrent and oxygen vacancy concentration. Source: Wang et al. [39]. © 2019 Willey.Figure 5.5 (a) The schematic charge transfer in particulate Ta₃N₅ photoanode. (b) The change of charge separation and transfer efficiency for Ta₃N₅ photoanode when the charge transfer and generation are improved gradually. Source: Wang et al. [45]. Licensed under CC BY 3.0 Unported.Figure 5.6 (a) The image and (b) the photoresponse (red curve) of branched 2D porous TiO₂ single‐crystal nanosheet photoelectrode. Insert (a) illustrates the photocharge transfer during PEC process. Source: Butburee et al. [71]. Reproduced with the permission from Wiley.Figure 5.7 (a) The surface state distribution characterization by cyclic voltammetry (CV) and the surface state related capacitance (C_ss). The different hematite photoelectrodes are compared including Ti doping, Al₂O₃ passivation, and H₂O₂ treatment. (b) The schematic illustration of PEC reaction via the surface states as intermediates. Source: From Wang et al. [8]. © 2016 Royal Society of Chemistry.Figure 5.8 The schematic illustration of cocatalyst design strategy based on a charge storage layer between the semiconductor and the effective cocatalyst layer.Figure 5.9 The schematic illustration of three different types of unbiased PEC water splitting systems. PA, PC, and PV represent photoanode, photocathode, and photovoltaic, respectively. The j–E curves represent their photoresponses in a three‐electrode system. The intersections (red dots) indicate the unbiased operation points.

5 Chapter 6Figure 6.1 Schematic illustration of photocatalytic oxygen evolution systems: (a) homogeneous and (b) heterogeneous configuration.Figure 6.2 Structures of (a) PS‐II‐OEC natural WOCs and (b) λ‐MnO₂, (c) Mn₄O₄L₆ core, and (d) Co₄O₄(Ac)₄(py)₄ artificial WOCs. Source: From McCool et al. [27]. © 2011 American Chemical Society.Figure 6.3 Ball‐and‐stick model of (a) Mn₄POM core, (b) polyhedral Mn₄POM, and (c) S₀ state of the natural OEC model. (d) Cycle diagram for the electron transfer within the S₀ → S₄ Kok cycle of the natural PS‐II‐OEC. (e) Photocatalytic oxygen evolution of Mn₄POM within the [Ru(bpy)₃]²⁺/Na₂S₂O₈ system. Source: From Al‐Oweini et al. [20]. © 2014 John Wiley & Sons.Figure 6.4 Illustration of the band positions of common semiconductor materials and the energy level toward water splitting.Figure 6.5 Comparison of electronic DOS of (a) 3D bulk semiconductor materials and LD semiconductor materials including (b) 2D, (c) 1D, and (d) 0D. The inset arrows on related models indicate the quantum confinement direction and dimensionalities. (e) Quantum size effect on band structure. (f) Schematic illustration of surface plasmon resonance excitation on metallic NPs.Figure 6.6 (a) TEM image of WO_2.83 NRs. (b) LSPR in 1D WO_2.83 NRs (experimental measurement and theoretical simulation). Source: Manthiram and Paul Alivisatos [55].Figure 6.7 (a–c) TEM images and (d) size distributions of Co₃O₄ NPs with different diameters (3, 10, and 40 nm). (e) The relationship between particle diameter and surface area. Inset: Images of NPs in the form of powder or dispersed in water. (f) Visible‐light‐ driven oxygen evolution of Co₃O₄ NPs with different diameters using Ru(bpy)₃²⁺ as the sensitization system. (g) Visible‐light‐driven oxygen evolution from various cobalt compounds placed on SBA‐15. Source: Reproduced with permission. Grzelczak et al. [69]. Copyright 2013, American Chemical Society.Figure 6.8 (a) TEM image and (b) Mott–Schottky plots for CoO NPs and micropowders. The flat band potentials are obtained via extrapolation method. (c) Band positions of CoO NPs and micropowders according to the band gaps and flat band potentials. Source: Reproduced with permission Liao et al. [77]. Copyright 2014, Nature Publishing Group.Figure 6.9 (a) TEM image quantum‐sized BiVO₄. (b) Comparison of the band position of nanoscale BiVO₄ and quantum‐sized BiVO₄. Source: Reproduced with permission. Sun et al. [89]. Copyright 2014, American Chemical Society.Figure 6.10 (a) Tungsten oxide single‐crystal nanosheets. (b,c) HRTEM images of WO₃, WO_3−x‐VT, and WO_3−x‐HT nanosheets. (d) Band position regulation of WO₃ nanosheets with oxygen vacancies. Source: From Yan et al. [58]. © 2015 John Wiley & Sons.Figure 6.11 (a) Representation of charge transfer between (001) and (110) facets. (b) Detachment and transfer of photoexcited charges in the BiOCl and defect‐rich BiOCl. (c) TEM image of the defect‐rich BiOCl ultrathin nanosheets. (d) Photocatalytic OER for BiOCl and defect‐rich BiOCl. Source: Reproduced with permission. Di et al. [107]. Copyright 2017, the Royal Society of Chemistry.Figure 6.12 The photocatalytic properties of LD materials including light absorption and charge transfer can be improved by doping engineering, active facet exposure, defect or vacancy creation, and LSPR. Hybrid LD materials with heterojunction can also be constructed in the form of 0D/1D, 1D/1D, 0D/2D, and 2D/2D configurations.Figure 6.13 (a,b) TEM images. (c) Time dependence of the O₂ evolution. (d) Proposed energy diagram for Co(OH)₂/TiO₂. Source: Reproduced with permission. Maeda et al. [110]. Copyright 2016, Wiley‐VCH.

6 Chapter 7Figure 7.1 PEC water splitting by n‐type TiO₂ photoanode for oxygen evolution reaction (OER) and Pt cathode for hydrogen evolution reaction (HER). The TiO₂ with band‐gap energy (E_g) of 3.0 eV is photoexcited under ultraviolet light irradiation. External voltage (ΔE_app) is applied between the electrodes to induce water photoelectrolysis.Figure 7.2 Current–potential curves for conventional water electrolysis in the dark. Over potentials (η) are required for HER and OER over each electrocatalyst electrode (η_HER + η_OER).Figure 7.3 Current–potential curves for water photoelectrolysis using photoanodes for OER and a cathode for HER at the current density (j) of 2 mA cm⁻². (a) Unbiased PEC water splitting and (b) PEC water splitting with externally applied voltage (ΔE_app). The ΔE_photo is the shift of the potential by using photoanodes in comparison with (c) anode electrocatalyst for OER. The absolute value of the current is equal between the series‐connected electrodes.Figure 7.4 (a) Current–potential curves of WO₃ photoanode in 0.1 mol l⁻¹ Na₂SO₄ (pH = 7) with 10 vol% methanol under UV irradiation (monochromatic light, λ = 365 nm) with different intensities of incident light. The light intensity (I₀) was controlled by using a neutral density filter. (b) Effect of the I₀ on the photocurrent density (j_photo) of the WO₃ photoanode in the linear sweep voltammetry. The j_photo was linearly increased with I₀ at each applied potential.Figure 7.5 (a) Flat band state and (b) band bending state of n‐type semiconductor. The recombination of the photoexcited e⁻ and h⁺ pair easily occurs in the flat band state. In contrast, the e⁻ and h⁺ pair is efficiently separated in the space charge layer (SCL). In the absence of surface states, the potential drop in the SCL (Δφ) is linear to the anodic shift of the applied potential from the flat band potential (E_fb).Figure 7.6 The pH dependence of the electrode potentials at 25 °C. The potentials of SHE and Ag/AgCl reference electrode are constant, but the potentials of RHE and the potentials for HER and OER are linearly increased by an increase in pH value with a slope of 59 mV (ln 10 × RT/F) at 25 °C.Figure 7.7 IPCE action spectra of rutile and anatase TiO₂ electrodes in 0.2 mol l⁻¹ Na₂SO₄ with phosphate buffer (pH = 7) at 0.9 V vs. RHE. The inset shows their diffuse reflectance UV–vis spectra using Kubelka–Munk function, F(R). Source: From Amano et al. [21]. © 2018 The Electrochemical Society.Figure 7.8 Mott–Schottky plots of WO₃ electrode in 0.1 mol l⁻¹ H₂SO₄ (pH = 1) in the dark to estimate the flat band potential (E_fb) and the donor density (N_D). The capacitance of the space charge layer (C_sc) was measured at 1 kHz with a sinusoidal amplitude of 10 mV in the dark. The inset shows the SEM image of the WO₃ electrode surface. Source: Adapted with permission Amano et al. [22]. Copyright 2011, Springer‐Verlag.Figure 7.9 Linear sweep voltammograms of the WO₃ electrode for (a) water oxidation in 0.1 mol l⁻¹ H₂SO₄ and (b) methanol oxidation in the solution with 10 vol% methanol under photoirradiation (solid j–E curves) and in the dark (dashed j–E curves). The applied potential where photocurrent response starts is denoted as E_onset. The E_fb is the value measured in Figure 7.8. Source: Based on Amano et al. [22].Figure 7.10 Band diagrams of n‐type semiconductors for PEC oxygen evolution: SrTiO₃, rutile TiO₂, monoclinic WO₃, α‐Fe₂O₃ (hematite), monoclinic scheelite‐type BiVO₄ (clinobisvanite) [28], and TaON [29] with E°(H⁺/H₂) and E°(O₂/H₂O). Here, the reported E_fb is considered as the conduction band (CB) minimum, although the CB minimum is more negative than E_fb by 0.1–0.3 eV. The valence band (VB) maximum is determined from the CB minimum and the optical E_g.Figure 7.11 Pourbaix diagram, which is a potential–pH equilibrium diagram, for (a) tungsten–water system and (b) iron–water system at 25 °C. The molar concentration of WO₄²⁻, Fe²⁺, and Fe³⁺ is 10⁻⁶ mol l⁻¹. The dashed lines show the potentials of HER and OER relative to pH value in water. Source: From Pourbaix [31]. © 1974, NACE.Figure 7.12 Schematic illustrations of photoexcited electron transport in photoanodes composed of (a) nanocrystalline particles with grain boundaries and (b) single‐crystalline materials with anisotropic nanostructures. Source: From Amano et al. [35]. © 2011 The Electrochemical Society.Figure 7.13 Crystal structure of WO₃·H₂O and cross‐sectional sideview SEM image of vertically aligned WO₃ flakes deposited on transparent conductive oxide (TCO) glass substrate for PEC water oxidation under visible‐light irradiation. The seed layer, which is WO₃ nanoparticles, is essential for heterogeneous nucleation of WO₃·H₂O flakes. The WO₃·H₂O flakes with two‐dimensional nanostructure were converted to monoclinic WO₃ by heat treatment. Source: From Amano et al. [36]. © 2010, RCS.Figure 7.14 Current–potential curves of (a) vertically aligned WO₃ flakes (blue dashed) and (b) horizontally stacked WO₃ flakes (black solid) deposited on TCO glass substrate in 0.1 mol l⁻¹ Na₂SO₄ (pH = 7) under visible‐light irradiation (λ > 400 nm). (A) Back‐side and (B) front‐side illumination were performed through the TCO glass substrate and the WO₃ layer, respectively. Chopped illumination was used to show the transient photocurrent response for water oxidation. Source: Based on Amano et al. [35].Figure 7.15 (a) Pictures of the thermally oxidized TiO₂ films (Ti plate calcined in air at 900 °C for two hours) and the films treated in H₂ stream at different temperatures (300–800 °C). (b) Effect of H₂ treatment temperature on the sheet resistance (R) and the donor density (N_D) of TiO₂ films. The R was measured by a four‐point probe. The N_D was measured by the Mott–Schottky analysis. (c) Effect of H₂ treatment temperature on the j_photo of TiO₂ films in 0.1 mol l⁻¹ H₂SO₄ (pH = 1). The j_photo for water oxidation was obtained in LSV measurement at 0.87 V vs. RHE under UV irradiation (λ > 300 nm). Source: Adapted with permission Amano et al. [38]. Copyright 2016, American Chemical Society.Figure 7.16 Schematic illustration of the PEC water oxidation process at the photoanode with cocatalyst layer: (a) conductive substrate, (b) n‐type semiconductor as a photoabsorber, (c) cocatalyst layer for OER, and (d) aqueous electrolyte solution. The number indicates the order of the PEC reaction process: (i) the generation of photoexcited e⁻–h⁺ pairs; (ii) charge separation, carrier diffusion, and carrier transport; and (iii) h⁺ transfer from semiconductor to water.Figure 7.17 Band alignments in three types of semiconductor heterojunctions: (a) straddling gap (type I), (b) staggered gap (type II), and (c) broken gap (type III).Figure 7.18 Schematic illustrations of (a) PEC cell for solar H₂ production using water vapor from the air over the sea and (b) vapor‐fed PEC water splitting system using a gas‐diffusion HER cathode, a proton exchange membrane (PEM), and a gas‐diffusion photoanode for OER. The photoanode is composed of a TiO₂ nanotube array decorated on porous Ti felt. The surface of TiO₂ nanotubes is coated with Nafion ionomer thin film for the gas‐phase operation. Source: (a) Adapted by permission of Wiley‐VCH Verlag. Amano et al. [53]; (b) Based on Amano et al. [54].Figure 7.19 Vapor‐fed water photoelectrolysis by porous SrTiO₃ photoanode |PEM| Pt‐carbon black cathode under humidified argon (3 vol% water vapor). The response of (a) photocurrent density and (b) the formation rate of H₂ evolved in the cathode compartment and O₂ evolved in the photoanode compartment at ΔE_app = 0.3 V under 365‐nm UV irradiation (I₀ = 42 mW cm⁻², photoanode area 2 cm²). The porous SrTiO₃ photoanode was coated by Nafion ionomer thin films for the gas‐phase operation. The evolved gas in each compartment was separated by a PEM and analyzed by on‐line gas chromatographs. Source: (a, b) Based on Amano et al. [54].

7 Chapter 8Figure 8.1 Different types of photocatalytic overall water splitting systems including (a) one‐step photoexcitation, (b) first‐generation Z‐scheme, (c) second‐generation Z‐scheme, and (d) third‐generation Z‐scheme. HEP: hydrogen evolution photocatalyst; OEP: oxygen evolution photocatalyst; HEC: hydrogen evolution cocatalyst; OEC: oxygen evolution cocatalyst; CB: conduction band; VB: valence band; E_g: energy band gap; NHE: normal hydrogen electrode; Ox: oxidant; Red: reductant.Figure 8.2 Representative material types for one‐step photocatalytic overall water splitting systems. (A) SrTiO₃ with 18 facets and selective deposition of HER and OER cocatalysts. Source: Mu et al. [68]. Copyright 2016, the Royal Society of Chemistry.Figure 8.3 Representative Z‐scheme types for photocatalytic overall water splitting. (a) First‐generation Z‐scheme coupling ZrO₂/TaON(HEP) and BiVO₄(OEP) with Fe³⁺/Fe²⁺ redox pairs as aqueous electron mediator and corresponding performance for 12 hours. Source: From Qi et al. [237]. © 2018 Elsevier.Figure 8.4 Different types of PEC for water splitting comprising (a) photoanode–cathode, (b) photocathode–anode, (c) photoanode–photocathode tandem cell, and (d) photovoltaic–photoanode (PV–PEC). Source: From Kim et al. [19]. © 2019 RCS.Figure 8.5 Photoanode–photocathode tandem cell for overall water splitting systems using (a) metal oxide‐based photoelectrodes (Cu₂O as HEP and Mo:BiVO₄ as OEP) and produced photocurrent density with stoichiometric H₂ and O₂ evolution. Source: Reproduced with permission. Pan et al. [368]. Copyright 2018, Macmillan Publishers Limited, part of Springer Nature.Figure 8.6 Photoanode–photocathode tandem cell for overall water splitting systems using (A) PEC system composed of IrO_x/n‐GaAs (photoanode) and Pt/Ti/Pt/Au/p‐GaAS (photocathode) and representative J–E curve. Source: Reproduced with permission. Kang et al. [395]. Copyright 2017, Macmillan Publishers Limited, part of Springer Nature.Figure 8.7 Representative PV–PEC devices for overall water splitting. (a) Inverted metamorphic multi‐junction (IMM) device structure with GaInP/GaInAs tandem PV cells coupled with RuO_x–Pt and J–V measurements. Source: From Young et al. [403]. © 2017 Springer Nature.Figure 8.8 Representative PV–PEC devices for overall water splitting. (a) System composed of single‐junction perovskite solar cell and a nanocone/Mo‐doped BiVO₄/Fe(Ni)OOH photoanode, and respective J–V curve for the tandem device. Source: From Qiu et al. [325]. © 2016 Yongcai Qiu.Figure 8.9 Representative artificial (wireless) PV–PEC devices for overall water splitting. (a) Tandem CH₃NH₃PbI₃ perovskite single‐junction solar cell with Co‐Ci incorporated H‐doped Mo/BiVO₄ photoanode and corresponding gas evolution with calculated STH efficiency. Source: From Kim et al. [421]. © 2015 American Chemical Society.

8 Chapter 9Figure 9.1 Schematic illustration of the natural photosynthesis (a) and the artificial photosynthesis (b) using semiconductor as the photocatalyst.Figure 9.2 Band positions of some semiconductor photocatalysts and the redox potentials of CO₂ reduction at pH 7 in aqueous solution. Source: Li et al. [12]. © 2014, Springer Nature.Figure 9.3 Schematic diagram of the slurry reactor (a) and the fixed bed reactor (b). Source: (a) Ola and Maroto‐Valer [17]. Licensed under CC BY 4.0. (b) Bakherad et al. [19]. © 2020, Royal Society of ChemistryFigure 9.4 (a) Schematic illustration of optical‐fiber photo reactor. (b) Light propagation in a TiO₂‐coated fiber reactor. Source: Wu et al. [20]. © 2008, Springer Nature.Figure 9.5 Dye‐sensitized photocatalytic reaction.Figure 9.6 Band alignment of bulk CdSe, CdSe QDs with a diameter of 2.5 nm, and TiO₂, as well as relevant redox potentials of CO₂ and H₂O. Source: Wang et al. [25]. © 2010, American Chemical Society.Figure 9.7 Schematic diagram of the reduction of CO₂ and water vapor into hydrocarbon fuels through a nanotube–catalyst array. Source: Varghese et al. [28]. © 2009, American Chemical Society..Figure 9.8 Semiconductor heterojunctions in the form of type I (a), type II (b), and type III (c).Figure 9.9 Schematic diagram of the photoexcitation process of AgBr/TiO₂ composite under visible‐light irradiation.Figure 9.10 Schematic illustration of TiO₂ with {001} and {101} surface heterojunction. Source: Yu et al. [31]. © 2014, American Chemical Society.Figure 9.11 Schematic illustration of the spatial separation of redox sites on the TiO₂ photocatalysts prepared without HF (a), by adding a moderate amount of HF (b), and by adding a high amount of HF (c).Figure 9.12 Schematic diagram of charge transfer in a Z‐scheme semiconductor–semiconductor composite.Figure 9.13 Schematic diagram of Z‐scheme BiVO₄/C/Cu₂O nanowire arrays. Source: Reproduced with permission. Kim et al. [32]. © 2018, American Chemical Society.Figure 9.14 Comparison of the energy band positions and the related redox reaction potentials of g‐C₃N₄ and ZnO. Source: Yu et al. [33]. © 2015, Royal Society of Chemistry.Figure 9.15 Schematic diagram of the solid–liquid interface structure.Figure 9.16 Potential comparison about the reduction of CO₂, H₂CO₃, and CO₃²⁻ ions into methanol. Source: Pan and Chen [38]. © 2007, Elsevier.Figure 9.17 Possible adsorption mechanism of CO₂ on TiO₂ surface. Source: Wu and Huang [40]. © 2010, Springer Nature.Figure 9.18 Schematic illustration of the charge transfer and separation in RGO–CdS nanorod system under visible‐light irradiation. Source: Yu et al. [41]. © 2014, Royal Society of Chemistry.Figure 9.19 Two proposed mechanisms for the photoreduction of CO₂ to methane: formaldehyde (a) and carbine (b) pathways. Source: Izumi [42]. © 2015, American Chemical Society.Figure 9.20 Photocatalytic reduction of CO₂ (86.65 kPa) by TiO₂ (a) and Pd(1%)‐TiO₂ (b). Source: Xiong et al. [44]. © 2017, Elsevier.Figure 9.21 Schematic mechanism of photocatalytic CO₂ reduction over CQDs/OCN‐x under visible‐light irradiation. Source: Li et al. [45]. © 2019, Springer Nature.

9 Chapter 10Figure 10.1 Schematic diagrams for PEC CO₂ reduction in water using a semiconductor as (a) photocathode, (b) photoanode, and (c) both photoanode and photocathode. (d) Schematic diagram for the device combining a photovoltaic cell with an efficient electrochemical catalyst for CO₂ reduction. Source: Zhang et al. [18]. © 2018, Springer Nature.Figure 10.2 (a) Scanning electron microscope (SEM) image of HA‐Co₃O₄. (b) Upper layer microflower morphology. (c) Lower layer rhombus nanorod morphology. (d) Transmission electron microscopy (TEM) of petals on the flower; Inset: selected area electron diffraction (SAED) pattern of petal region. (e) High‐resolution transmission electron microscopy (HRTEM) of petal region. (f) Formate yields of HA‐Co₃O₄ under PEC and EC under different negative potentials. Crystallographic modeling of Co₃O₄ (g) {12}, (h) {001}, (i) {110}, and (j) {111} facets with side view (left) and oblique view (right). Blue, light blue, and red spheres represent Co³⁺, Co²⁺, and O²⁻, respectively. Source: Huang et al. [54]. © 2013, American Chemical Society.Figure 10.3 (a) Linear sweep voltammetry of the BCN_3.0 electrodes loaded with or not loaded with cocatalysts. (b) Products analyses of photoelectrochemical reduction of CO₂ over cocatalyst‐loaded BCN_3.0 electrodes. Source: Sagara et al. [26]. © 2016, Elsevier.Figure 10.4 Periodic table depicting the primary reduction products in CO₂‐saturated aqueous electrolytes on metal and carbon electrodes. Source: White et al. [2]. © 2015, American Chemical Society.Figure 10.5 Schematic representations for (a) Co^II complex and (b) Fe^II complex for PEC reduction of CO₂. Source: Chen et al. [83]. © 2015, American Chemical Society.Figure 10.6 Schematic of (a) the ruthenium dye‐sensitized TiO₂ nanoparticles with adsorbed CODH enzyme, which catalyzes the reduction of CO₂ to CO. Source: Woolerton et al. [89]. © 2010, American Chemical SocietyFigure 10.7 Schematic image of (a) NiO–RuRe as photocathode and CoO_x/TaON as photoanode. Source: Sahara et al. [30]. © 2016, American Chemical Society.

10 Chapter 11Figure 11.1 (a) Schematic illustrations of different pathways for N₂ reduction, including the dissociative pathway, associative alternating pathway, and associative distal pathway. Source: (a) Shipman et al. [13]. © 2017, Elsevier.Figure 11.2 (a) Schematic of the plasmon excitation‐based photocatalytic N₂ reduction. (b) TEM image of the Au/TiO₂−OV NSs. (c) EPR spectra of four catalysts of TiO₂, TiO₂−OV, Au/TiO₂, and Au/TiO₂−OV. (d) Detected NH₃ concentrations of four catalysts. Source: (a–d) Adapted from Yang et al. [30]. © 2018, American Chemical Society.Figure 11.3 (a) Schematic of the synthesis process of engineering NVs into g‐C₃N₄. (b) ESR and (c) TPD spectra of the prepared g‐C₃N₄ and V−g‐C₃N₄. Source: (a–c) Adapted from Dong et al. [43]. © 2015, Royal Society of Chemistry.Figure 11.4 (a) Schematic photocatalytic N₂ reduction on ultrathin MWO‐1 nanowires. Adsorption configurations of N₂ molecules with different charge dispersions on (b) defect‐rich W₁₈O₄₉, and (c) Mo‐doped W₁₈O₄₉. (d) O K‐edge XAS spectra of different photocatalysts. (e) Schematic of the PCET process for photocatalytic N₂ fixation. (f) Photocatalytic NH₃ yield rates with MWO-1. Source: (a–f) Adapted from Zhang et al. [53]. © 2018, American Chemical Society.Figure 11.5 (a) and (b) HAADF−STEM images and (c) EDX mapping of A‐SmOCl. (d) ESR signals and (e) O K‐edge XAS spectra of different photocatalysts. (f) In situ DRIFT spectra recorded in the N₂ reduction process. Source: (a–f) Hou et al. [61]. © 2019, Elsevier.Figure 11.6 (a) SEM and (b) TEM images of the GaN NWs. (c) TEM image of Ru (5 wt%) decorated GaN NWs. Inset: the diameter distributions of Ru nanoclusters. (d) Schematic of the Schottky barrier between Ru clusters and n‐type GaN NWs. (e) Schematic illustration for the InGaN/GaN with five segments of InGaN on the template of GaN nanowire. (f) NH₃ evolution rates of various photocatalysts under visible‐light illumination. Source: (a–f) Li et al. [74]. © 2017, John Wiley & Sons.Figure 11.7 (a) Schematic illustration of photocatalytic cell for N₂ fixation. (b) and (c) HRTEM images of hollow Au–Ag₂O, the inset is the corresponding FFT of the nanoparticle. (d) NH₃ yields and solar‐to‐ammonia (STA) efficiencies of different photocatalysts. (e) NH₃ yields of Au–Ag₂O under various operating conditions. Source: (a–e) Nazemi et al. [82]. © 2019, Elsevier.Figure 11.8 (a) Schematic of N₂ reduction on the aerophilic–hydrophilic interface. (b) Droplet shapes of the liquid and N₂ bubble on different interfaces. (c) Interfacial water molecule spectra on the surface of Au-PTFE/TS . (d) NH₃ yield rates and FEs on Au/TS and Au−PTFE/TS at different potentials. Source: (a–d) Zheng et al. [89]. © 2019, Elsevier.Figure 11.9 (a) Schematic of the synthesis steps for the Au/end−CeO₂ heterojunction. (b) HAADF−STEM image and the related elemental mapping. Mechanism for N₂ photo‐fixation on the Au/end−CeO₂ heterojunction. The hot carrier separation behaviors on (c) the Au/end−CeO₂ and (d) the core@shell nanostructures. Source: (a–d) Jia et al. [111]. © 2019, American Chemical Society.Figure 11.10 (a) Schematic of TiO_2−xH_y/Fe catalyst for dual‐temperature‐zone photo‐thermal NH₃ synthesis. (b) High‐resolution STEM image of TiO_2−xH_y/Fe catalyst. (c) Steady‐state non‐equilibrium temperature distribution and dual‐temperature‐zone NH₃ synthesis on TiO_2−xH_y/Fe. (d) LTDs between hot Fe and cooling TiO_2−xH_y. (e) SERS mapping of the spatial dispersion of TiO_2−xH_y, Fe, and the adonitol and the detected local LTD. (f) The NH₃ concentrations produced at different apparent catalyst temperatures. (g) Successive light‐on/off measurement of photo‐thermal NH₃ synthesis. (h) The impressive equilibrium‐beyond reactivity of TiO_2−xH_y/Fe at different pressures. Source: (a–h) Mao et al. [118]. © 2019, Elsevier.Figure 11.11 (a) HRTEM, (b) elemental mapping, and (c) HAADF−STEM images of Mo−PCN. (d) Time‐resolved fluorescence kinetics. (e) LT−FTIR spectra for N₂ adsorption. (f) Charge density difference of Mo−PCN with adsorbed N₂. Source: (a–f) Guo et al. [119]. © 2019, Royal Society of Chemistry.Figure 11.12 (a) Schemcatic of designed Mo₂Fe₆S₈−Sn₂S₆ biomimetic chalcogel. Source: (a) Adapted from Banerjee et al. [122]. © 2015, American Chemical Society.

11 Chapter 12Figure 12.1 (a) UV–vis DRS and (b) N₂ adsorption isotherms at 77 K for MIL‐125‐NH₂ and NiO/MIL‐125‐NH₂. Source: Isaka et al. [24]. © 2018, Royal Society of Chemistry.Figure 12.2 Ni K‐edge (a) XAFS and (b) FT‐EXAFS spectra of NiO/MIL‐125‐NH₂. Source: Isaka et al. [24]. © 2018, Royal Society of Chemistry.Figure 12.3 (a) TEM image, (b) HAADF‐STEM image, and (c‐f) EDX mappings of NiO/MIL‐125‐NH₂. Source: Reproduced with permission from Isaka et al. [24].Figure 12.4 (a) Time course of photocatalytic H₂O₂ production catalyzed by MIL‐125‐NH₂ in the presence and absence of TEOA and visible‐light irradiation (λ > 420 nm). (b) Time courses of photocatalytic H₂O₂ production catalyzed by MIL‐125‐NH₂, NiO/MIL‐125‐NH₂, and Pt/MIL‐125‐NH₂. Source: (a) Isaka et al. [24]. © 2018, Royal Society of Chemistry.Figure 12.5 (a) Time course of TEOA oxidation product formation under visible‐light (λ > 420 nm) irradiation for MIL‐125‐NH₂. (b) Mass spectrum of the peak after photoirradiation. (c,d) Reported oxidation products of TEOA in literatures. (e) Plausible product of TEOA oxidation. Source: Isaka et al. [24]. © 2018, Royal Society of Chemistry.Figure 12.6 Time courses of H₂O₂ and benzaldehyde production of (a) MIL‐125‐NH₂ and (b) NiO/MIL‐125‐NH₂ dispersed in an acetonitrile solution of benzyl alcohol under visible‐light irradiation (λ > 420 nm). Source: Isaka et al. [24]. © 2018, Royal Society of Chemistry.Figure 12.7 Time courses of H₂O₂ (15 mM) decomposition dissolved in 5.0 ml of acetonitrile suspension of 5.0 mg of MIL‐125‐NH₂ and NiO/MIL‐125‐NH₂ at 313 K. Source: Isaka et al. [24]. © 2018, Royal Society of Chemistry.Figure 12.8 EPR spectral of suspensions containing DMPO and (a) MIL‐125‐NH₂ or (b) NiO/MIL‐125‐NH₂ under visible‐light irradiation (λ > 420 nm). Source: (a) Isaka et al. [24]. © 2018, Royal Society of Chemistry.Figure 12.9 (a) Digital photographs of two‐phase systems composed of an aqueous phase and a benzyl alcohol phase containing MIL‐125‐NH₂ (left) and MIL‐125‐Rn (n = 4 and 7, right). (b) Photocatalytic H₂O₂ production in the two‐phase system. Source: Isaka et al. [28]. © 2019, John Wiley & Sons.Figure 12.10 (a) XRD patterns and (b) UV–vis DRS for MIL‐125‐NH₂, MIL‐125‐R4, and MIL‐125‐R7. Source: Isaka et al. [28]. © 2019, John Wiley & Sons.Figure 12.11 FE‐SEM images of (a,c) MIL‐125‐NH₂ and (b,d) MIL‐125‐R7 (a,b) before and (c,d) after three hours of photoirradiation (λ > 420 nm) reaction in the two‐phase system composed of benzyl alcohol (5.0 ml) and water (2.0 ml). Source: Reproduced with permission from Isaka et al. [28].Figure 12.12 TEM images of (a,c) MIL‐125‐NH₂ and (b,d) MIL‐125‐R7 (a,b) before and (c,d) after three hours of photoirradiation (λ > 420 nm) reaction in the two‐phase system composed of benzyl alcohol (5.0 ml) and water (2.0 ml). Source: Reproduced with permission from Isaka et al. [28].Figure 12.13 TG‐DTA measurement of (a,b) MIL‐125‐NH₂, (c,d) MIL‐125‐R4, and (e,f) MIL‐125‐R7. Chemical structures of linkers in (g) MIL‐125‐NH₂, alkylated linker in (h) MIL‐125‐R4, and (i) MIL‐125‐R7. Source: Isaka et al. [28]. © 2019, John Wiley & Sons.Figure 12.14 (a) Water adsorption isotherms at 298 K for MIL‐125‐NH₂, MIL‐125‐R4, and MIL‐125‐R7. The water contact angles of (b) MIL‐125‐NH₂, (c) MIL‐125‐R4, and (d) MIL‐125‐R7. Source: (a) Isaka et al. [28]. © 2019, John Wiley & Sons; (b–d) Reproduced with permission from Isaka et al. [28].Figure 12.15 (a) Digital photograph of MIL‐125‐NH₂ (left) and MIL‐125‐R7 (right) dispersed into the two‐phase system; aqueous phase (2.0 ml) was observed on top of the benzyl alcohol phase (5.0 ml). (b) Time courses of H₂O₂ production under photoirradiation (λ > 420 nm) in the two‐phase system catalyzed by 5.0 mg of catalysts. Source: (a) Reproduced with permission from Isaka et al. [28]; (b) Isaka et al. [28]. © 2019, John Wiley & Sons.Figure 12.16 Time courses of benzaldehyde formation under photoirradiation (λ > 420 nm) of the two‐phase system composed of benzyl alcohol (5.0 ml) and water (2.0 ml) catalyzed by 5.0 mg of catalysts. Source: Isaka et al. [28]. © 2019, John Wiley & Sons.Figure 12.17 XRD patterns of MIL‐125‐NH₂ and MIL‐125‐R7 after three hours of photoirradiation (λ > 420 nm) reaction in the two‐phase system composed of benzyl alcohol (5.0 ml) and water (2.0 ml). Source: Isaka et al. [28]. © 2019, John Wiley & Sons.Figure 12.18 Recycling tests of H₂O₂ production under photoirradiation (λ > 420 nm) of the two‐phase system composed of benzyl alcohol (10.0 ml) and water (4.0 ml) catalyzed by 10.0 mg of MIL‐125‐NH₂ (blue) and MIL‐125‐R7 (orange). Source: Isaka et al. [28]. © 2019, John Wiley & Sons.Figure 12.19 (a) Time courses of H₂O₂ production under photoirradiation (λ > 420 nm) of the two‐phase system composed of benzyl alcohol (5.0 ml) and water (2.0, 5.0, and 10.0 ml) catalyzed by 5.0 mg of MIL‐125‐R7. (b) Time courses of H₂O₂ production under photoirradiation (λ > 420 nm) of the two‐phase system composed of benzyl alcohol (5.0 ml) and water (2.0 ml) at different pH values (0.3, 1.3, 2.1, and 6.7) catalyzed by 5.0 mg of MIL‐125‐R7. (c) Time courses of H₂O₂ production under photoirradiation (λ > 420 nm) of the two‐phase system composed of benzyl alcohol (5.0 ml) and an aqueous phase (2.0 ml, deionized water or saturated NaCl aqueous solution) catalyzed by 5.0 mg MIL‐125‐R7. Source: Isaka et al. [28]. © 2019, John Wiley & Sons.Figure 12.20 N₂ adsorption isotherms at 77 K for MIL‐125‐NH₂, MIL‐125‐R4, and MIL‐125‐R7. Source: Isaka et al. [28]. © 2019, John Wiley & Sons.Figure 12.21 Photocatalytic H₂O₂ production with (a) linker‐alkylated MOF: MIL‐125‐R7 and (b) cluster‐alkylated MOF: OPA/MIL‐125‐NH₂. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.Figure 12.22 (a) XRD patterns and (b) UV–vis DRS of MIL‐125‐NH₂ and OPA/MIL‐125‐NH₂. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.Figure 12.23 N₂ adsorption isotherms at 77 K for MIL‐125‐NH₂ and OPA/MIL‐125‐NH₂. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.Figure 12.24 (a) TG and (b) DTA profiles of OPA/MIL‐125‐NH₂. (c) Chemical structures of alkylated clusters in OPA/MIL‐125‐NH₂. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.Figure 12.25 FTIR spectra of (a) MIL‐125‐NH₂, OPA/MIL‐125‐NH₂, and (b) OPA. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.Figure 12.26 (a) XPS spectra of Ti 2p in MIL‐125‐NH₂ and OPA/MIL‐125‐NH₂. (b) XPS spectra of P 2p in MIL‐125‐NH₂ and OPA/MIL‐125‐NH₂ before and after etching. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.Figure 12.27 (a) Water contact angle of OPA/MIL‐125‐NH₂. (b) Time courses of H₂O₂ production of OPA/MIL‐125‐NH₂ under photoirradiation (λ > 420 nm) in the two‐phase system. Source: (a) Kawase et al. [31]. © 2019, Royal Society of Chemistry; (b) Reproduced with permission from Kawase et al. [31].Figure 12.28 Time courses of benzaldehyde production of OPA/MIL‐125‐NH₂ under photoirradiation (λ > 420 nm) in the two‐phase system. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.Figure 12.29 Time courses of H₂O₂ production under photoirradiation (λ > 420 nm) of a single‐phase system composed of an acetonitrile solution (5.0 ml) of BA (1.0 ml) catalyzed by 5.0 mg of catalysts. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.Figure 12.30 Recycling tests of MIL‐125‐NH₂, MIL‐125‐R7, and OPA/MIL‐125‐NH₂. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.Figure 12.31 XRD patterns of OPA/MIL‐125‐NH₂ before and after reaction. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.Figure 12.32 N₂ adsorption isotherms at 77 K for OPA/MIL‐125‐NH₂ before and after the reaction. Source: Kawase et al. [31]. © 2019, Royal Society of Chemistry.

12 Chapter 13Figure 13.1 (a) The kinetic progress of methaneactivation on thermocatalysis and photocatalysis methods, (b) reaction mechanism of photocatalysis, and (c) reaction mechanism of photoelectrochemical catalysis. Source: Song et al. [2].Figure 13.2 (a–d) Photoexcitation and subsequent relaxation processes following the illumination of a metal nanoparticle with a laser pulse and characteristic time scales. Source: Brongersma et al. [28]Figure 13.3 (A) Schematic (a) a conventional vacuum line equipped with pressure gage; (b) joint; (c) small hole for thermo‐couple; (d) catalyst bed; (e) UV‐reflection mirror; (f) Xe lamp. drawing of the fixed bed photo‐reactor. Source: Yoshida et al. [46]Figure 13.4 (a) Difference on activation energy between photocatalysis and thermocatalysis. Source: Chen et al. [5], licensed under CC BY 4.0Figure 13.5 (a) Proposed mechanisms of photooxidation of CH₄ on TiO₂. Source: Li et al. [26] © 2018, American chemical society

13 Chapter 14Figure 14.1 Composition of biomass.Figure 14.2 (a) Reaction process images, quantification, and distribution of products obtained from the photocatalytic depolymerization of birch lignin. (b) Proposed mechanism for β‐O‐4 bond cleavage in the photocatalytic conversion of lignin over the Zn₄In₂S₇ catalyst. Source: Reprinted with permission from Lin et al. [27].Figure 14.3 Photographs taken before (a) and after (b) precipitation of lignin during photoelectrocatalytic oxidation of 500 ppm lignin at different times, (c) Fourier transform infrared (FTIR) spectra of lignin and modified lignin, and (d) intermediates analyzed using HPLC. Source: Reprinted with permission from Tian et al. [48].Figure 14.4 Illustration of experimental reactor used for photoreforming cellulose to hydrogen via combined photocatalysis and acid hydrolysis. Source: Zou et al. [56].Figure 14.5 Photothermally promoted cleavage of β‐1,4‐glycosidic bonds of cellulose on Ir/HY catalyst. Source: Reprinted with permission from Zhang et al. [57].Figure 14.6 Schematic representation of the photocatalytic system for the H₂ evolution by water splitting over irradiated Pt/TiO₂ in the presence of cellulose as the sacrificial agent. Source: Speltini et al. [62], licensed under CC BY 3.0.Figure 14.7 Photocatalytic H₂ production using activated ^NCNCN_x (5 mg) and Ni bis(diphosphine) (NiP) (50 nmol) with purified lignocellulose components (100 mg) in potassium phosphate (KPi) solution (0.1 M, pH 4.5, 3 ml) under AM 1.5 G irradiation for 24 hours at 25 °C. Source: Kasap et al. [68].Figure 14.8 Schematic illustration of the lignocellulose structure and photocatalytic valorization of native lignin. Source: Reprinted with permission from Wu et al. [70].Figure 14.9 (a) Scanning electron microscope (SEM) image of sample Bi₂WO₆; (b) Time‐online photocatalytic performance toward selective oxidation of glycerol to DHA over Bi₂WO₆. Source: (a) Reprinted with permission from Zhang et al. [74]; (b) Zhang et al. [74].Figure 14.10 A simple solar‐induced hybrid direct glycerol fuel cell consists of a Pt cathode, a Na‐Pi buffer electrolyte with glycerol as fuel and NiPi/Pi–Fe₂O₃ as a photoanode, and the possible photo‐generated charging process of glycerol process of glycerol oxidation over NiPi/Pi–Fe₂O₃. Source: Chong et al. [97].Figure 14.11 SEM image of (a) W:BiVO₄ and (b) pTTh films. (c) The energy level diagram of the dual‐photoelectrode PFC. Source: (a, b) Modified with permission from Zhang et al. [36]; (c) Zhang et al. [36].Figure 14.12 Schematic configuration and electron transfer processes of PEC glucose/glucose fuel cell employing TiO₂/ITO photoanode and ITO cathode upon incorporation of UV light and MB. Insets show SEM images of TiO₂/ITO and structures of MB and LMB. Source: Zhao et al. [104].Figure 14.13 A plausible reaction mechanism of PEC selective aerobic oxidation of benzyl alcohols. Source: Zhang et al. [112].Figure 14.14 A photoelectrochemical cell for HMF reduction. Inset is the SEM image showing the surface morphologies of Ag_gd. Source: (a) Roylance et al. [116]; (b) Reprinted with permission from Roylance et al. [116].

14 Chapter 15Figure 15.1 Schematic illustration of electron–hole pair generation in a semiconductor upon light irradiation. Possible pathways are labeled in 1– 4, where 1, reduction; 2, oxidation; 3, volume recombination; and 4, surface recombination; A, electron acceptor, and B, electron donor. Source: Linsebigler et al. [4].Figure 15.2 Schematic illustration of different photocatalytic water splitting systems. (a) One‐step photoexcitation or single‐component photocatalytic system. (b) Photocatalytic system with type‐II heterojunction. (c) Two‐step photoexcitation or Z‐scheme photocatalytic system. Source: Chen et al. [6].Figure 15.3 Possible configurations of CO₂ absorption on the surface of photocatalysts. Source: Liu et al. [12].Figure 15.4 Bandgap energies and the band edge positions of some commonly reported photocatalysts as well as the products derived from photocatalytic CO₂ reduction with reference to normal hydrogen electrode (NHE). Source: Tu et al. [10].Figure 15.5 (a) Photoanode–HEC cathode, (b) photocathode–OEC anode, (c) photoanode–photocathode tandem cell, and (d) photoanode–photovoltaic (PEC‐PV) tandem cell. Source: Kim et al. [1].Figure 15.6 Schematic illustration of side‐irradiated water splitting reactor. Source: Takata et al. [23].Figure 15.7 Schematic illustration of top‐irradiated water splitting reactor. Source: Kudo et al. [25].Figure 15.8 (a) Schematic illustrations of inner‐irradiated reactor in lab scale. Source: Wei et al. [27].Figure 15.9 Schematic illustration of a twin photo‐reactor system. Source: Sasaki et al. [29].Figure 15.10 Schematic illustration of photocatalytic water splitting panel. Source: (a) Reproduced with permission Goto et al. [30]. Copyright 2018, Elsevier; (b) Goto et al. [30].Figure 15.11 Schematic illustration of (a) slurry reactor, (b) internally illuminated reactor, and (c) optical fiber reactor. Source: Ola et al. [35], licensed under CC BY 4.0.Figure 15.12 Schematic diagram of photocatalytic CO₂ reduction in a continuous gas flow fixed bed reactor. Source: Kong et al. [7].Figure 15.13 Schematic diagram of PEC water splitting system in the configuration of (a) n‐type photoanode‐HEC and (b) p‐type photocathode‐OEC. Source: Ahmed et al. [40].Figure 15.14 Schematic diagram of PEC water splitting devices: (a) with membrane and (b) without membrane. (c) Photograph of an integrated membrane‐free device with internal wiring. Source: Reproduced with permission Jin et al. [41]. Copyright 2014, Royal Society of Chemistry.Figure 15.15 Schematic diagram of PEC CO₂ reduction system. Source: Cheng et al. [42].Figure 15.16 Large‐scale reactor for photocatalytic H₂ production containing immobilized Pt/g‐C₃N₄ working under natural sunlight. Source: Reproduced with permission Schröder et al. [43]. Copyright 2015, Wiley.Figure 15.17 (a) Schematic illustration of synthesis protocol of SrTiO₃:La,Rh/Au/BiVO₄:Mo Z‐scheme photocatalyst sheets using particle transfer method. (b) Electron transfer mechanism of SrTiO₃:La,Rh/Au/BiVO₄:Mo Z‐scheme system. (c) Photograph of the ink used for screen printing and the corresponding printed photocatalyst sheets. Source: (a, c) Reproduced with permission Wang et al. [30]. Copyright 2016, Nature Publishing Group; (b) Wang et al. [30].Figure 15.18 (a) False‐colored SEM image of Si/TiO₂ nanotree arrays photocatalyst sheets. (b) Photographs of Si/TiO₂ photocatalyst sheets. (c) Charge transfer mechanism in Si/TiO₂ photocatalyst sheets. Source: Reproduced with permission Liu et al. [44]. Copyright 2013, American Chemical Society.Figure 15.19 (a) Wired PEC cell and monolithic wireless cell of Co‐Bi/3jn a‐Si/NiMoZn system. Source: Reece et al. [45]. Copyright 2011, American Association for the Advancement of Science.Figure 15.20 (a) SrTiO₃‐based artificial leaf with Cu_xO as HER co‐catalysts and CoPi as OER co‐catalysts. Source: Reproduced with permission Chen et al. [48]. Copyright 2017, American Chemical Society.