A nanocomposite cathode is composed of a mixed H + /e À conducting BaCe x Y y Co z O 3d (P-BCCY) phase, a mixed O 2À /e À conducting BaCo x Ce y Y z O 3d (M-BCCY) phase, and a mixed O 2À /e À conducting BaCoO 3-d (BC) phase. The P-BCCY phase could promote proton diffusion, the M-BCCY phase could facilitate oxygen ion diffusion, and the BC phase could enhance the electronic conduction of the electrode; the interfaces between the three phases in nano-domain greatly increases the number of active sites for electrochemical reactions.

Electrochemical water splitting is a critical energy conversion process for producing clean and sustainable hydrogen; this process relies on low‐cost, highly active, and durable oxygen evolution reaction/hydrogen evolution reaction electrocatalysts. Metal cations (including transition metal and noble metal cations), particularly high‐valence metal cations that show high catalytic activity and can serve as the main active sites in electrochemical processes, have received special attention for developing advanced electrocatalysts. In this review, heterogenous electrocatalyst design strategies based on high‐valence metal sites are presented, and associated materials designed for water splitting are summarized. In the discussion, emphasis is given to high‐valence metal sites combined with the modulation of the phase/electronic/defect structure and strategies of performance improvement. Specifically, the importance of using advanced in situ and operando techniques to track the real high‐valence metal‐based active sites during the electrochemical process is highlighted. Remaining challenges and future research directions are also proposed. It is expected that this comprehensive discussion of electrocatalysts containing high‐valence metal sites can be instructive to further explore advanced electrocatalysts for water splitting and other energy‐related reactions.

An ideal solid oxide fuel cell (SOFC) cathode should meet multiple requirements, i.e., high activity for oxygen reduction reaction (ORR), good conductivity, favorable stability, and sound thermo‐mechanical/chemical compatibility with electrolyte, while it is very challenging to achieve all these requirements based on a single‐phase material. Herein, a cost‐effective multi‐phase nanocomposite, facilely synthesized through smart self‐assembly at high temperature, is developed as a near‐ideal cathode of intermediate‐temperature SOFCs, showing high ORR activity (an area‐specific resistance of ≈0.028 Ω cm2 and a power output of 1208 mW cm−2 at 650 °C), affordable conductivity (21.5 S cm−1 at 650 °C), favorable stability (560 h operation in single cell), excellent chemical compatibility with Sm0.2Ce0.8O1.9 electrolyte, and reduced thermal expansion coefficient (≈16.8 × 10−6 K−1). Such a nanocomposite (Sr0.9Ce0.1Fe0.8Ni0.2O3–δ) is composed of a single perovskite main phase (77.2 wt%), a Ruddlesden–Popper (RP) second phase (13.3 wt%), and surface‐decorated NiO (5.8 wt%) and CeO2 (3.7 wt%) minor phases. The RP phase promotes the oxygen bulk diffusion while NiO and CeO2 nanoparticles facilitate the oxygen surface process and O2− migration from the surface to the main phase, respectively. The strong interaction between four phases in nanodomain creates a synergistic effect, leading to the superior ORR activity.

The development of clean and efficient energy conversion and storage systems is becoming increasingly vital as a result of accelerated global energy consumption. Solid oxide fuel cells (SOFCs) as one key class of fuel cells have attracted much attention, owing to their high energy conversion efficiency and low emissions. However, some serious problems appeared because of the scorching operating temperatures of SOFCs (800−1000 °C), such as poor thermomechanical stability and difficult sealing, resulting in a short lifespan and high cost of SOFCs. Therefore, lowering the operating temperature of SOFCs to mid-range and even low range has become one of the main goals for SOFC development in the recent years. Looking for new cathode materials with high electrocatalytic activity and robust stability at relatively low temperatures is one of the essential requirements for intermediateto-low-temperature SOFCs (ILT-SOFCs). During the past 15 years, we put considerable efforts into the development of alternative cathode materials for ILT-SOFCs. In this review, we give a summary of our progress from such efforts. We first summarize several strategies that have been adopted for developing cathode materials with high activity and durability toward reducing operating temperatures of SOFCs. Then, our new ideas and progress on cathode development with respect to activity and stability are provided. Both the cathodes of oxygen-ion-conducting SOFCs and protonic-conducting SOFCs are discussed. In the end, we outline the opportunities, challenges, and future approaches for the development of cathodes for ILT-SOFCs.

New reduced-temperature ceramic fuel cells with dual-ion conducting electrolyte and triple conducting double perovskite cathode.

Reversible protonic ceramic cells (RePCCs) can facilitate the global transition to renewable energy sources by providing high efficiency, scalable, and fuel‐flexible energy generation and storage at the grid level. However, RePCC technology is limited by the lack of durable air electrode materials with high activity toward the oxygen reduction/evolution reaction and water formation/water‐splitting reaction. Herein, a novel nanocomposites concept for developing bifunctional RePCC electrodes with exceptional performance is reported. By harnessing the unique functionalities of nanoscale particles, nanocomposites can produce electrodes that simultaneously optimize reaction activity in both fuel cell/electrolysis operations. In this work, a nanocomposite electrode composed of tetragonal and Ruddlesden–Popper (RP) perovskite phases with a surface enriched by CeO2 and NiO nanoparticles is synthesized. Experiments and calculations identify that the RP phase promotes hydration and proton transfer, while NiO and CeO2 nanoparticles facilitate O2 surface exchange and O2‐ transfer from the surface to the major perovskite. This composite also ensures fast (H+/O2‐/e‐) triple‐conduction, thereby promoting oxygen reduction/evolution reaction activities. The as‐fabricated RePCC achieves an excellent peak power density of 531 mW cm‐2 and an electrolysis current of −364 mA cm‐2 at 1.3 V at 600 °C, while demonstrating exceptional reversible operation stability of 120 h at 550 °C.

Research data are not shared.

Solid oxide fuel cells (SOFCs), which can directly convert chemical energy stored in fuels into electric power, represent a useful technology for a more sustainable future. They are particularly attractive given that they can be easily integrated into the currently available fossil fuel infrastructure to realize an ideal clean energy system. However, the widespread use of the SOFC technology is hindered by sulfur poisoning at the anode caused by the sulfur impurities in fossil fuels. Therefore, improving the sulfur tolerance of the anode is critical for developing SOFCs for use with fossil fuels. Herein, a novel, highly active, sulfur‐tolerant anode for intermediate‐temperature SOFCs is prepared via a facile impregnation and limited reaction protocol. During synthesis, Ni nanoparticles, water‐storable BaZr0.4Ce0.4Y0.2O3− δ (BZCY) perovskite, and amorphous BaO are formed in situ and deposited on the surface of a Sm0.2Ce0.8O1.9 (SDC) scaffold. More specifically, a porous SDC scaffold is impregnated with a well‐designed proton‐conducting perovskite oxide liquid precursor with the nominal composition of Ba(Zr0.4Ce0.4Y0.2)0.8Ni0.2O3− δ (BZCYN), calcined and reduced in hydrogen. The as‐synthesized hierarchical architecture exhibits high H2 electro‐oxidation activity, excellent operational stability, superior sulfur tolerance, and good thermal cyclability. This work demonstrates the potential of combining nanocatalysts and water‐storable materials in advanced electrocatalysts for SOFCs.