Magnetic Field Enhancement of the Electrocatalytic Oxygen Evolution Reactivity in Amorphous Cobalt Oxide Thin Films

Photoelectrochemical water-splitting presents a promising avenue to generate sustainable molecular hydrogen as a fuel source and molecular oxygen as a biproduct on the commercial scale. The kinetic and thermodynamic barrier behind this process is the oxygen evolution reaction (OER), which involves the transfer of 4 protons and 4 electrons to form the oxygen-oxygen bond. This study investigates the effects of a directional, uniform, and tunable externally applied magnetic field on the oxygen evolution reaction (OER) activity of the phosphate-based and borate-based amorphous cobalt oxide thin films. These films are of particular interest since they consist of abundant earth materials, are low-cost, operate at neutral pH, and have self-healing properties. A magneto-electrochemical setup was designed and 3D printed to investigate how varying strengths of a magnetic field influence the OER performance in these catalysts. Increases in OER catalytic activity of up to an order of magnitude, as defined by Tafel Slope analysis, were observed at the highest attainable field strength of 1.4 T. The observed magnetic field enhancement was found to be reproducible across various films of the same thickness and was found to be most significant in CoPi films of 5mC thickness. The results offer unique insights into the capabilities of magnetic field enhancing OER catalysis in amorphous cobalt oxide films, and further supports the yet-inconclusive intramolecular oxygen radical (O*) coupling mechanism for the oxygen evolution rate determining step between adjacent Co oxo units.