development of sustainable energy conversion and storage technologies. [1] Nowadays, the electrolysis of oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and carbon dioxide reduction reaction (CO 2 RR) is being extensively researched. [2] The conversion efficiencies of these electrochemical reactions are critical to the performance of sustainable energy devices, including fuel cells, metal-air batteries, and electrolyzers. [3] Particularly, ORR is the cathode reaction of fuel cells which are characterized by a higher energy efficiency than that of conventional combustion engines. [4] ORR and OER occur at the gas electrode of a rechargeable metal-air battery. [5] In the production of electro-fuels (e.g., H 2 or CO), HER and CO 2 RR serve as the cathode reactions in electrolyzers with H 2 O and CO 2 as the reactants, respectively. [6] The development of high-performance electrocatalysts is critical for the mass adoption of those sustainable energy applications. [7] Carbon-supported nonprecious metals (C@NPMs) have recently attracted significant attention for the promotion of the above-mentioned reactions during electrolysis owing to their low cost and potentially high activity. [8] Carbon frameworks can be easily modified and can take the form of various nanostructures, such as 1D carbon nanotubes (CNTs), [9] 2D graphene, [10] and 3D porous carbons. [11] The coupling of nonprecious metals with carbons can mitigate the corrosion issues of these metals under harsh electrolysis conditions (e.g., strong alkaline/acidic electrolytes and oxidative potentials), and reduce agglomeration by enhancing the dispersion of the metal moieties. [12] In addition, the coupling can promote charge transfer between the carbon and the metal components, thereby tuning the electronic structure for catalysis. [13] Thus, the carbon support not only works as a conductive substrate but also interacts electronically with the metal species, modifying the electronic/ electrochemical properties of the composite. [14] The catalytic properties of C@NPMs can be further optimized by introducing heteroatom dopants, engineering topological defects, modulating metal size, tuning the carbon shell, and coupling multimetals. [15] Owing to the tremendous efforts of the research community in this field, C@NPMs have seen significant advancements. For instance, Fe or Co coupled with N-doped carbon, i.e., FeNC and CoNC are one of the most promising ORR electrocatalysts to replace precious Pt in both acidic and alkaline electrolytes. [16] The development of sustainable energy conversion and storage devices, such as fuel cells, metal-air batteries, and electrolyzers is highly dependent on the catalytic oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and carbon dioxide reduction reaction (CO 2 RR). Carbon-supported nonprecious metals (C@NPMs) with variable metal sizes (single atom, cluster, and nanoparticle) are attracting significant interest for catalyzin...

Summary Thermodynamic analysis is performed on a conceptual oxygen permeation membrane reactor driven by concentrated solar energy (heat) for isothermal H2O splitting for the purpose of solar fuel derivation. By way of a plug‐flow reactor model, kinetic and thermodynamic factors responsible for conversion rate, reactor dimension, and solar‐to‐fuel efficiency are analyzed for the case of pump‐assisted and methane‐assisted scenarios. The pump‐assisted case achieves the same solar‐to‐fuel efficiency (2.9% at 1500 °C) as isothermal solar thermochemical cycling, while the methane‐assisted case attains much higher efficiencies at much lower temperatures, whose net solar‐to‐fuel efficiency reaches 63% at around 900 °C. The theoretical framework developed in this study can be applied to the solar thermochemical splitting of other gases such as CO2 and can be further extended to the co‐splitting of H2O and CO2 for syngas production driven by solar energy only (i.e., without the participation of hydrocarbon fuels). Copyright © 2015 John Wiley & Sons, Ltd.

No abstract