The high reaction temperature required for chemical looping in water splitting presents challenges in terms of producing stable oxygen carrier materials (OCMs). The currently available materials are generally prepared by a deposition method through which iron oxides and refractory supports are spatially separated, thus having low activity and stability. Here, we report CoFeAlO_x as an OCM, in which the active phase of the CoFe alloy and the parent spinel support are homogeneously mixed into a solid solution. Using a variety of characterization techniques, we studied the exsolution and dissolution effects of the CoFe alloy on the spinel support in a chemical looping redox cycle and found that the exsolution process can be tailored by the reduction level, which determines the interface structure. When reduced by CO, the exsolved particles were similar to the deposited analogues, showing obvious sintering. However, for the sample reduced by CO and CO₂, the exsolved CoFe alloy can be embedded into the support, with it re-emerging fresh and confined at each reduction period. After 20 cycles, it showed a high hydrogen production rate and outstanding stability, demonstrating that the controllable exsolution could significantly improve the high temperature redox performance. Based on these results, this study also provides a new dimension for designing improved redox materials for chemical looping, calcium looping, or solar-driven thermochemical applications.

The sustainable production of chemicals and fuels from abundant solar energy and renewable carbon sources provides a promising route to reduce climate-changing CO₂emissions and our dependence on fossil resources. Here, we demonstrate solar-powered formate production from readily available biomass wastes and CO₂feedstocks via photoelectrochemistry. Non-precious NiOOH/α-Fe₂O₃and Bi/GaN/Si wafer were used as photoanode and photocathode, respectively. Concurrent photoanodic biomass oxidation and photocathodic CO₂reduction towards formate with high Faradaic efficiencies over 85% were achieved at both photoelectrodes. The integrated biomass-CO₂photoelectrolysis system reduces the cell voltage by 32% due to the thermodynamically favorable biomass oxidation over conventional water oxidation. Moreover, we show solar-driven formate production with a record-high yield of 23.3 μmol cm⁻²h⁻¹as well as high robustness using the hybrid photoelectrode system. The present work opens opportunities for sustainable chemical and fuel production using abundant and renewable resources on earth—sunlight, biomass and CO₂.

Proton ceramic electrochemical cells (PCECs) have attracted significant attention from governmental institutions and research societies as an emerging technology for energy conversion and storage. As some of the representative high-temperature electrochemical devices, PCECs have achieved impressive progress and become an influential research direction in the energy field. They exhibit wide-ranging application prospects and offer numerous possibilities for the subsequent production of valuable chemical products at intermediate temperatures, due to their remarkable flexibility and reliability. The development of efficient, stable, and long-life elementary PCEC devices relies heavily on the exploitation of new materials and structural designs. In this paper, we provide a general review of the mechanisms of proton transport and the fundamental operating principles of PCECs. We comprehensively summarize strategies used to improve electrochemical performance in the past few years, encompassing the state-of-the-art electrode and electrolyte materials, novel approaches for structural optimization, and innovative developments in electrochemical cell devices. Importance is given to the presentation of various applications of PCECs, including H₂O electrolysis, CO₂/H₂O co-conversion in the electrolysis mode, and the synthesis of high-value chemicals such as CH₄ and CO through CO₂ electrochemical conversion with proton donors like H₂, C₂H₆, or NH₃ (conceptualized). Consequently, we provide a future perspective on PCEC commercialization and highlight the existing challenges that need to be addressed.