Distinguishing the four mechanistic routes of magnetic-field-enhanced CO2 electroreduction: From spin chemistry to mass transport

Electrochemical CO 2 reduction (CO 2 RR) can convert carbon dioxide into carbon monoxide, formate, and multicarbon fuels, but its selectivity, energy efficiency, and stability remain limited by sluggish interfacial kinetics, competing hydrogen evolution, and mass-transport gradients. Magnetic regulation has recently emerged as a non-contact strategy that can act through several physically distinct routes. This mini review therefore separates four mechanistic routes that have been proposed or demonstrated and that are often conflated: radical-pair singlet–triplet interconversion, field-induced polarization of active sites or magnetic domains, Lorentz-force-driven magnetohydrodynamic transport, and field-free spin control based on chirality-induced spin selectivity, topological surface states, and coordination-controlled spin states. Reported catalyst families are compared by material class, target product, magnetic-field configuration, and performance outcome. Representative systems include Sn and Bi catalysts for formate, Ni-based catalysts for CO, and Cu-based interfaces, radical-modified metal–organic frameworks, and chiral Ag for C 2+ products. Particular attention is paid to controls needed to distinguish genuine spin effects from transport, heating, and geometric artifacts. The review closes with design rules for mechanism-matched field orientation, field-free spin control, operando validation, and a net-energy and techno-economic framework for flow electrolyzers. Reported fields span from tens of millitesla to 2 T, with substantial gains in C 2+ and CO selectivity under selected conditions. However, to our knowledge, reported energy savings remain confined to cell-level analyses because auxiliary magnet, cooling, and pumping loads have not been fully measured. Overall, this work provides a mechanistic framework for rationally exploiting magnetic and spin effects in CO 2 RR and guides the design of more selective, energy-efficient, and stable electrocatalytic systems.