The Perfect Imperfections in Electrocatalysts

type perovskite oxide by noble metal doping is a propitious route to enhance the OER/ORR bifunctionality for zinc-air battery (ZAB). The perovskite oxides can be tuned by calcination at different temperatures to alter the oxygen vacancy, GB fraction and overall reactivity. The oxygen defects, unsaturated coordination environment and GBs can turn a relatively less active nanostructure into an efficient redox active catalyst by imbibing plenty of electrochemically active sites. Obviously, the crystalline GB interface is a prerequisite for effective electron flow, which is also applicable for the crystalline surface oxide shell on metal alloy core of the nanoparticles (NPs). The oxygen vacancy of two-dimensional (2D) perovskite oxide can be made reversible by the A-site termination of the nanosheets, facilitating the reversible entry and exit of a secondary phase during the redox processes. In several instances, the secondary phases have been observed to introduce the right proportion of structural defects and orbital occupancies for adsorption and desorption of reaction intermediates. Also, heterogeneous interfaces can be created by wrapping the perovskite oxide with negatively charged surface by layered double hydroxide (LDH) can promote the OER process. In another approach, ion intercalation at the 2D heterointerfaces steers the interlayer spacing that can influence the mass diffusion. Similar to anion vacancy, controlled formation of the cation vacancies can be achieved by exsolving the B-site cations of perovskite oxides to surface anchored catalytically active metal/alloy NPs. In case of the alloy electrocatalysts, incomplete solid solution by two or more mutually immiscible metals results in heterogeneous alloys having differently exposed facets with complementary functionalities. From the future perspective, new categories of defect structures including the 2D empty spaces or voids leading to undercoordinated sites, the multiple interfaces in heterogeneous alloys, antisite defects between anions and cations, and the defect induced inverse charge transfer should bring new dimensionalities to this riveting area of research.