New Undisputed Evidence and Strategy for Enhanced Lattice-Oxygen Participation of Perovskite Electrocatalyst through Cation Deficiency Manipulation.

Oxygen evolution reaction (OER) is a key half-reaction in many electrochemical transformations, and efficient electrocatalysts are critical to improve its kinetics which is typically sluggish due to its multielectron-transfer nature. Perovskite oxides are a popular category of OER catalysts, while their activity remains insufficient under the conventional adsorbate evolution reaction scheme where scaling relations limit activity enhancement. The lattice oxygen-mediated mechanism (LOM) has been recently reported to overcome such scaling relations and boost the OER catalysis over several doped perovskite catalysts. However, direct evidence supporting the LOM participation is still very little because the doping strategy applied would introduce additional active sites that may mask the real reaction mechanism. Herein, a dopant-free, cation deficiency manipulation strategy to tailor the bulk diffusion properties of perovskites without affecting their surface properties is reported, providing a perfect platform for studying the contribution of LOM to OER catalysis. Further optimizing the A-site deficiency achieves a perovskite candidate with excellent intrinsic OER activity, which also demonstrates outstanding performance in rechargeable Zn-air batteries and water electrolyzers. These findings not only corroborate the key role of LOM in OER electrocatalysis, but also provide an effective way for the rational design of better catalyst materials for clean energy technologies.

Building Ruddlesden-Popper and Single Perovskite Nanocomposites: A New Strategy to Develop High-Performance Cathode for Protonic Ceramic Fuel Cells.

Here a new strategy is unveiled to develop superior cathodes for protonic ceramic fuel cells (PCFCs) by the formation of Ruddlesden-Popper (RP)-single perovskite (SP) nanocomposites. Materials with the nominal compositions of LaSrx Co1.5 Fe1.5 O10- δ (LSCFx, x = 2.0, 2.5, 2.6, 2.7, 2.8, and 3.0) are designed specifically. RP-SP nanocomposites (x = 2.5, 2.6, 2.7, and 2.8), SP oxide (x = 2.0), and RP oxide (x = 3.0) are obtained through a facile one-pot synthesis. A synergy is created between RP and SP in the nanocomposites, resulting in more favorable oxygen reduction activity compared to pure RP and SP oxides. More importantly, such synergy effectively enhances the proton conductivity of nanocomposites, consequently significantly improving the cathodic performance of PCFCs. Specifically, the area-specific resistance of LSCF2.7 is only 40% of LSCF2.0 on BaZr0.1 Ce0.7 Y0.2 O3- δ (BZCY172) electrolyte at 600 °C. Additionally, such synergy brings about a reduced thermal expansion coefficient of the nanocomposite, making it better compatible with BZCY172 electrolyte. Therefore, an anode-supported PCFC with LSCF2.7 cathode and BZCY172 electrolyte brings an attractive peak power output of 391 mW cm-2 and excellent durability at 600 °C.

High-Performance Perovskite Composite Electrocatalysts Enabled by Controllable Interface Engineering.

Single-phase perovskite oxides that contain nonprecious metals have long been pursued as candidates for catalyzing the oxygen evolution reaction, but their catalytic activity cannot meet the requirements for practical electrochemical energy conversion technologies. Here a cation deficiency-promoted phase separation strategy to design perovskite-based composites with significantly enhanced water oxidation kinetics compared to single-phase counterparts is reported. These composites, self-assembled from perovskite precursors, comprise strongly interacting perovskite and related phases, whose structure, composition, and concentration can be accurately controlled by tailoring the stoichiometry of the precursors. The composite catalyst with optimized phase composition and concentration outperforms known perovskite oxide systems and state-of-the-art catalysts by 1-3 orders of magnitude. It is further demonstrated that the strong interfacial interaction of the composite catalysts plays a key role in promoting oxygen ionic transport to boost the lattice-oxygen participated water oxidation. These results suggest a simple and viable approach to developing high-performance, perovskite-based composite catalysts for electrochemical energy conversion.

Catalysis based on ferroelectrics: controllable chemical reaction with boosted efficiency.

Catalysts, which can accelerate chemical reactions, show promising potential to alleviate environmental pollution and the energy crisis. However, their wide application is severely limited by their low efficiency and poor selectivity due to the recombination of photogenerated electron-hole pairs, the back-reaction of interactants. Accordingly, ferroelectrics have emerged as promising catalysts to address these issues with the advantages of promoted light adsorption, boosted catalytic efficiency as a result of their intrinsic polarization, suppressed electron-hole pair recombination, and superior selectivity via the ferroelectric switch. This review summarizes the recent research progress of catalytic studies based on ferroelectric materials and highlights the controllability of catalytic activity by the ferroelectric switch. More importantly, we also comprehensively highlight the underlying working mechanism of ferroelectric-controlled catalysis to facilitate a deep understanding of this novel chemical reaction and guide future experiments. Finally, the perspectives of catalysis based on ferroelectrics and possible research opportunities are discussed. This review is expected to inspire wide research interests and push ferroelectric catalysis to practical applications.

Direct evidence of boosted oxygen evolution over perovskite by enhanced lattice oxygen participation.

The development of oxygen evolution reaction (OER) electrocatalysts remains a major challenge that requires significant advances in both mechanistic understanding and material design. Recent studies show that oxygen from the perovskite oxide lattice could participate in the OER via a lattice oxygen-mediated mechanism, providing possibilities for the development of alternative electrocatalysts that could overcome the scaling relations-induced limitations found in conventional catalysts utilizing the adsorbate evolution mechanism. Here we distinguish the extent to which the participation of lattice oxygen can contribute to the OER through the rational design of a model system of silicon-incorporated strontium cobaltite perovskite electrocatalysts with similar surface transition metal properties yet different oxygen diffusion rates. The as-derived silicon-incorporated perovskite exhibits a 12.8-fold increase in oxygen diffusivity, which matches well with the 10-fold improvement of intrinsic OER activity, suggesting that the observed activity increase is dominantly a result of the enhanced lattice oxygen participation.