IrO₂ exhibits good stability but limited electrocatalytic activity for oxygen evolution reaction in acid. Defect engineering is an effective strategy to improve the intrinsic ability of electrocatalysts by tailoring their electronic structure. Herein, we have successfully synthesized IrO₂/Ir heterophase with compressive strain and metal vacancies via a simple substitution-etching method. In virtue of the solubility of Cr in strong alkali, metal vacancies could be formed at surface after etching Cr-doped IrO₂/Ir in alkali, which leaded to modulated electronic structure. Meanwhile, the substitution of Cr with smaller atom radius would induce the formation of compressive strain and the relocated atoms made the d-band center shifted. With the regulated electronic structure and tuned d-band center, the obtained electrocatalyst only needed 285 mV to reach 10 mA·cm⁻² in 0.1 M HClO₄. Reaction kinetic has been rapidly accelerated as indicated by the smaller Tafel slope and charge transfer resistance. Theoretical calculations revealed that the d-band center and charge density distribution have been regulated with the introduction of defects in IrO₂/Ir, which significantly decreased the free energy barrier of rate determining step. This work provides a valuable reference to design effective and defects-rich electrocatalysts.

Dispersing atomic metals on substrates provides an ideal method to maximize metal utilization efficiency, which is important for the production of cost-effective catalysts and the atomic-level control of the electronic structure. However, due to the high surface energy, individual single atoms tend to migrate and aggregate into nanoparticles during preparation and catalytic operation. In the past few years, various synthetic strategies based on ultrafast thermal activation toward the effective preparation of single-atom catalysts (SACs) have emerged, which could effectively solve the aggregation issue. Here, we highlight and summarize the latest developments in various ultrafast synthetic strategy with rapid energy input by heating shockwave and instant quenching for the synthesis of SACs, including Joule heating, microwave heating, solid-phase laser irradiation, flame-assisted method, arc-discharge method and so on, with special emphasis on how to achieve the uniform dispersion of single metal atoms at high metal loadings as well as the suitability for scalable production. Finally, we point out the advantages and disadvantages of the ultrafast heating strategies as well as the trends and challenges of future developments.

Gas-involving electrochemical reactions, like oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), are critical processes for energy-saving, environment-friendly energy conversion and storage technologies which gain increasing attention. The development of according electrocatalysts is key to boost their electrocatalytic performances. Dramatic efforts have been put into the development of advanced electrocatalysts to overcome sluggish kinetics. On the other hand, the electrode interfaces-architecture construction plays an equally important role for practical applications because these imperative electrode reactions generally proceed at triple-phase interfaces of gas, liquid electrolyte, and solid electrocatalyst. A desirable architecture should facilitate the complicate reactions occur at the triple-phase interfaces, which including mass diffusion, surface reaction and electron transfer. In this review, we will summarize some design principles and synthetic strategies for optimizing triple-phase interfaces of gas-involving electrocatalysis systematically, based on the electrode reaction process at the three-phase interfaces. It can be divided into three main optimization directions: exposure of active sites, promotion of mass diffusion and acceleration of electron transfer. Furthermore, we especially highlight several remarkable works with comprehensive optimization about specific energy conversion devices, including metal-air batteries, fuel cells, and water-splitting devices are demonstrated with superb efficiency. In the last section, the perspectives and challenges in the future are proposed.