Magnetic fields enhance mass transport during electrocatalytic reduction of CO2

Abstract

The selectivity of electrocatalytic reduction of CO 2 (CDR) is dictated not only by the intrinsic reactivity of the catalyst but also by the transport of reactants to the catalyst (i.e., mass transport). Current methods for increasing mass transport in CDR rely upon either (1) mechanical agitation or (2) use of gas-diffusion electrodes and are unable to eliminate concentration polarization completely. This work demonstrates that magnetic fields orthogonal to the ionic current (i.e., the Lorentz force) can be used to increase mass transport during CDR by generating convective flow in the fluid, thus modifying the observed selectivity of CDR. This increase in mass transport leads to a corresponding increase in current densities (up to 1.3× higher than the analogous system with no B → -field or agitation) and increased selectivity of CDR relative to the hydrogen evolution reaction (up to 2.5× higher than the system with no B → -field or agitation). • During CDR, magnetic fields (B-fields) generate convective currents in the fluid • The convection generated by B-fields decreases pH gradients during electrolysis • The magnitude of the B-field effect is dictated by the structure of the cathode • B-fields decrease the cost of operating a CO 2 electrolyzer by ∼10% At high current densities (>100 mA/cm 2 ), the electrocatalytic reduction of CO 2 (CDR) can be limited by mass transport, resulting in decreased selectivity for CDR relative to the reduction of protons to hydrogen. Common approaches to increase mass transport for CDR rely upon either (1) gas-diffusion electrodes or (2) mechanical agitation. This work demonstrates that magnetic fields acting through the Lorentz force can increase mass transport during CDR. Magnetic fields generate convective currents by the Lorentz force acting on ions moving during electrolysis and decreases the cost of operating a CO 2 electrolyzer (by ∼10% in this work). Magnetic fields parallel to the surface of an electrode can be used to increase mass transport during electrocatalytic reduction of CO 2 .