Understanding the activity and stability of flame-made Co3O4 spinels: A route towards the scalable production of highly performing OER electrocatalysts

Abstract

Carbon-free production of hydrogen from renewable energy sources is readily attainable via electrochemical water splitting. Increasing the fraction of H2 generated by such environmentally friendly routes requires, however, further progress in electrode design to overcome the limited stability and activity of earth-abundant electrocatalysts. Herein, we report the multiscale engineering of the properties of Co3O4 electrocatalysts for oxygen evolution reaction (OER), revealing insights into the close interplay between activity and stability. The surface chemistry and physical properties of Co3O4 electrodes such as Co2+/Co3+ ratio, fractal features, and electron conductivity are modulated by a highly scalable one-step hot-aerosol synthesis. Optimized Co3O4 electrodes are obtained with a high mass-specific current density for OER of 642 A g−1 at 400 mV overpotential, which can be boosted to 1947 A g−1 at industrially-relevant elevated electrolyte temperature of 80 °C. Through operando Raman measurements, we reveal the in-situ transformation of the as-synthesized cobalt oxide moieties to oxyhydroxide species, identifying their role as catalytic active sites for OER. The potential of these earth-abundant electrocatalysts and their scalable preparation approach are demonstrated with a custom-designed electrolyzer, achieving a very high mass-specific current density of 800 A g−1 at 400 mV overpotential and more than 12 h stable operation.