Revealing the mass transfer of proton donors for tailoring hydrogen evolution coupled with manganese electrodeposition

Abstract

Hydrogen evolution reaction (HER) has traditionally been considered as an undesirable side reaction that becomes increasingly problematic with the rise of concentration polarization, posing the primary bottleneck in energy saving and consumption reduction in Mn metallurgy. For this reason, a brand-new rotating cylindrical cathode (RCC) was proposed to overcome the inherent limitations of a static plate electrode for metallic Mn deposition. In this work, we conducted multidimensional operando investigations to elucidate the peculiar HER performance in the Mn electrodeposition system. The results reveal that the commonly accepted idea that an increase in conjugate HER leads to a decrease in Mn deposition efficiency is incomplete when considering the mass transfer of NH₄⁺. Through theoretical calculations and dynamic analyses, we demonstrate that NH₄⁺ outcompetes H₂O as an extraneous proton donor, significantly catalyzing the proton-electron transfer process of HER, which is sensitive to applied potential and mass transfer conditions. By studying the adsorption, interaction, and desorption of intermediates close to the RCC interface, we have elucidated the synergistic catalytic action of NH₄⁺ on HER and Mn electrodeposition. This work offers valuable insights into manipulating HER dynamics to address current challenges in metal deposition, while also presenting novel opportunities for predicting and practically applying RCC in electrometallurgy.