Controlled electrochemical synthesis of bimetallic cobalt–manganese borate (CoMnB_i) thin layer for enhanced clean oxygen generation reaction: Experimental and theoretical investigation

There is a pressing need to develop facile synthesis methodologies and efficient earth-abundant electrocatalysts for accelerating oxygen evolution reaction (OER) that facilitates various purposes ranging from efficient green hydrogen to clean oxygen generation. In this work, a facile electrochemical deposition method was employed to synthesize bimetallic cobalt-manganese borate (x%-Co-Mn-B_i) electrocatalysts on fluorine-doped tin oxide (FTO) substrate. The bimetallic borate electrocatalysts were characterized as synthesized using XRD, SEM, EDS, and XPS studies. The electrochemical performance for OER was demonstrated using a 3-electrode electrochemical cell set-up. Due to metal-metal synergistic effects and other supporting factors, the 30%-Co-Mn-B_i exhibited the lowest overpotential among the un-annealed samples, followed by 40%-Co-Mn-B_i. However, when the samples were annealed at different temperatures, 40%-Co-Mn-B_i annealed at 200 °C showed the best overall OER performance with the least Tafel slope of 72.5 mV/dec, lower charge transfer resistance, a high electrochemical surface area, excellent turnover frequency, moderate faradaic efficiency in addition to convincing long-term stability for OER application. The results were further validated using theoretical Density Functional Theory (DFT) treatment which inferred that 30%-Co-Mn-B_i exhibits the lowest overpotential for oxygen generation reaction. This work provides a concrete and comprehensive strategy for the controlled synthesis of varying stoichiometric thin-layer bimetallic borates for efficient oxygen production with reduced usage of expensive cobalt.