Enhancement of Electrocatalysis through Magnetic Field Effects on Mass Transport

Abstract The catalytic conversion of small molecules into fuels using electrons is essential to achieve a sustainable and carbon-neutral society. However, the performance of current electrocatalytic processes needs significant improvement. Magnetic field effects on electrocatalysis have recently gained attention due to the substantial enhancement of the oxygen evolution reaction on ferromagnetic catalysts. In this context, it is crucial to carefully characterize how magnetic fields affect mass transfer of charged reactants and products at the interfacial level, a phenomenon that occurs even on non-magnetic electrodes and is often overlooked. In this paper, we quantify the primary source of magnetic field effects on mass transport using a specifically designed magneto-electrochemical system. We find that the Lorentz force acting on the electrolyte ions induces a vortex-type motion around the catalyst surface, improving the mass transport. This effect is not limited to reactions involving gas-phase reactants/products. The enhancement caused by the mass transport effect is small in the case of reactions with high reactant availability, such as the oxygen evolution reaction (OER) but it is particularly advantageous where the availability is hindered, such as oxygen reduction reaction (ORR). We report activity boosts of more than 50% in the ORR induced by the magnetic field on non-magnetic interfaces. Our results allow direct visualization and quantification of the motion of OH − ions under a magnetic field, highlighting the relevance of magnetic field effects on electrocatalytic processes, especially the diffusion limited reactions, and offer new opportunities for developing more efficient and sustainable energy conversion technologies.