Tuning Morphology and Cation Selection for OER and ORR Bifunctional Catalytic Activity in Nano (nA1/n)Co2O4

Reducing carbon emissions to meet the carbon neutrality goal while providing global energy demand on the terawatt level promotes the pursuit of clean energy technologies such as photovoltaics, wind turbines, and the production of hydrogen from water in a sustainable manner. Water splitting to produce hydrogen via the electrolysis pathway is considered a promising direction toward carbon-free energy production, especially considering the potential utilization of renewable (wind, solar, geothermal) and nuclear energy for the electricity source. A key research challenge lies in improving the energy efficiency for converting electricity to hydrogen over various operating conditions. With this regard, designing and developing economically feasible, earth-abundant, inexpensive, efficient electrocatalysts for the oxygen evolution reaction (OER) is a critical research factor. Even further, searching for electrocatalysts that can boost both the OER and the oxygen reduction reaction (ORR) simultaneously is crucial for deploying hydrogen production in a usable form, e.g., fuel cells. Conventional research focuses on noble metal (Pt, Ir, Ru, etc.) based electrocatalysts, which cannot meet the future goal of large-scale deployment due to their low abundance and high cost. Therefore, there have been intense efforts in exploring low-cost transition metal-based electrocatalysts, among which cobalt oxides are promising for both OER and ORR. Early this year, A. H. Li, et al. reported in Nat. Catal. a significant enhancement of the stability of Co3O4 spinel oxide by inserting Mn into the lattice. According to their report, the catalyst lifetime in solid acid (pH=1) environment was extended by two orders of magnitude. In fact, the exploration space can be enormously expanded by introducing compositional complexity in the cobalt spinel oxide system. In such scenarios, the rich variety of local geometry and coordination environment as induced by the compositional complexity enriches the type and/or strength of orbital hybridization. Consequently, the electronic structure could be tuned to control the reactivity of those active elements. Understanding how various local environments (geometry, distortion, coordination) are linked to electrocatalytic performance is therefore crucial, which then further necessitates a clear picture of the nature and tunability of the family's structure across length scales.