Ample Lewis Acidic Sites in Mg2B2O5 Facilitate N2 Electroreduction through Bonding-Antibonding Interactions.

ABSTRACT

Extensive research on the electrochemical nitrogen reduction reaction (NRR) has put forward a sound list of potential catalyst materials with properties inducing N2 adsorption, protonation, and reduction. However, rather than a random selection of catalysts, it is essential to understand the vitals in terms of orbital orientation and charge distribution that actually manipulate the rate-determining steps of NRR. Realizing these factors, herein we have explored a main group earth-abundant Mg-based electrocatalyst Mg2B2O5 for NRR due to the abundance of Lewis acid sites in the catalyst favoring the bonding-antibonding interactions with the N2 molecules. Positron annihilation studies indicate that the electronic charge distribution within the catalyst has shallow surface oxygen vacancies. These features in the catalyst enabled a sound Faradaic efficiency of 46.4% at -0.1 V vs reversible hydrogen electrode for the selective NH3 production in neutral electrolyte. In situ Fourier transform infrared suggests a maximum N-N bond polarization at -0.1 V and detected H-N-H and -NH2 intermediates during the course of the NRR on the catalyst surface. In a broader picture, the biocompatibility of Mg2+ diversifies the utility of this catalyst material in N2/biofuel cell applications that would certainly offer a green alternative toward our goal of a sustainable society.