(Invited) Glassy Carbon Electrodes Modified with Micromagnets: Magnetoelectrocatalysis of HER

Abstract

Electrode kinetics for the hydrogen evolution reaction (HER) on glassy carbon electrodes are inherently slow. Voltammetric responses are marked by large overpotentials η and small exchange current densities j0.HER rates are markedly increased on glassy carbon electrodes modified with composites of Nafion® and siloxane coated micromagnets. Comparison of linear sweep voltammograms of glassy carbon electrodes modified with either Nafion films or composites of magnetized iron oxide microparticles identifies enhanced HER rates where magnetic gradients are established. For magnetized 1 \U0001d707m γ-Fe2O3 microparticles in Nafion, η is decreased by 0.191 ± 0.019 V at 0.4 mA cm-2 compared to Nafion films. This corresponds to an energetic advantage of -18.4 kJ/mol and a 40-fold increase in j0. For magnetized 5 \U0001d707m Fe3O4 microparticles in Nafion, η is decreased by 0.28 V at 0.4 mA cm-2, which corresponds to an energetic advantage of -27 kJ/mol and 230-fold increase in exchange current. HER rate on platinum electrodes is unchanged for Pt electrodes modified with Nafion films and with composites of magnetized micromagnets in Nafion. Enhancements are not due to either magnetohydrodynamics or mediation as there is no bulk solvent volume in Nafion to convect and siloxane coating renders the iron oxide microparticles chemically and electrochemically inert. Voltammetry for glassy carbon electrodes modified with Nafion films and with composites of Nafion and demagnetized microparticles are comparable.The chemistry of magnetized and demagnetized composites are the same; the rate enhancements arises from the physical impact of the magnetic gradients in the magnetized composites.The enhanced rate for HER on glassy carbon arises through magnetoelectrocatalysis.Work is undertaken at the University of Iowa. The National Science Foundation (NSF CHE-1309366 and NSF CHE-0809745) and the Army Research Office (W911NF-19-1-0208 (74912-CH-II)) supported these projects.