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Understanding the mechanism of proton conduction is of utmost importance for the development of novel materials. It is generally accepted that proton diffusion in protonic conductors occur via the Grotthuss‐type mechanism assisted by water molecules [81–83]. Moreover, hydrogen separation is driven by the hydrogen partial pressure difference across the membrane.

Proton conductivity has been observed in different types of materials. Perovskite‐type oxide ceramics are known to be proton conductors since the early 1980s. In general, perovskite structure with a general formula A²⁺B⁴⁺O₃ (type II–IV), where A is Ba and B is Zr, Tb, Ce, or Th, exhibits the best proton conductivities being higher than 10⁻² S cm⁻¹, the lowest activation energies for proton transport, and high negative hydration enthalpies [78]. In particular, ceramic materials such SrCeO₃, BaCeO₃, or SrZrO₃ are the most widely studied high‐temperature proton‐conducting perovskite‐type materials. Zirconate‐based materials are more interesting than cerates regarding their application in CO₂ environments because of their higher stability under reducing atmospheres; however, they present an important grain boundary resistance and a high sintering temperature is needed to produce dense samples. In order to overcome the disadvantage of both families of materials, solid solutions of doped BaCeO₃ and BaZrO₃ have been developed by different research groups [84–87].

The reader is referred to other literature sources to dwell into other examples of proton conducting materials such as rare earth oxides, rare earth ortho‐niobates and tantalates, rare earth tungstates, phosphates, and pyrochlores [75, 78, 88, 89].

Because of the low electronic conductivity, the abovementioned materials do not present a sufficiently high hydrogen permeation flux for their integration in practical applications. Composite membranes composed by two phases, an electronic and a protonic phase, have been developed in the past years to overcome this problem, obtaining promising permeation values [90–93].