Magneto-Electrochemical Deposition of Faceted Copper Microcrystals for Nitrate-to-Ammonia Electrocatalysis

Electrochemical deposition is a facile and effective method for the in situ growth of metal electrocatalysts; however, it is difficult to optimize their morphology and performance due to the kinetics-controlled growth at high current density. Herein, we develop a new magneto-electrochemical deposition technique to prepare the faceted microcrystals of copper (Cu) catalysts for highly efficient electrocatalytic nitrate-to-ammonia conversion. The field generates a Lorentz force on the flow of Cu ions near the cathode surface, which retards the mass transport to predeposited Cu particles and increases the density of Cu nucleation sites due to the magnetohydrodynamics (MHD) effect. This further slows down the growth rates of individual Cu particles at even high current density, and as-prepared Cu catalysts change from low-crystalline microspheres to thermodynamic-controlled faceted microcrystals. Especially, these Cu microcrystals show a very high exposure of (111) facet, which provides an energy-efficient reaction pathway for nitrate reduction. The magneto-electrochemically deposited Cu microcrystals exhibit a high Faradaic efficiency of >95% for nitrate-to-ammonia conversion with an excellent stability over 60 h, which indicates that the magneto-electrochemical deposition provides a promising way to the design and synthesis of high-quality electrocatalysts for advanced catalytic applications.