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

Extensiveresearch on the electrochemical nitrogen reduction reaction(NRR) has put forward a sound list of potential catalyst materialswith properties inducing N-2 adsorption, protonation, andreduction. However, rather than a random selection of catalysts, itis essential to understand the vitals in terms of orbital orientationand charge distribution that actually manipulate the rate-determiningsteps of NRR. Realizing these factors, herein we have explored a maingroup earth-abundant Mg-based electrocatalyst Mg2B2O5 for NRR due to the abundance of Lewis acid sitesin the catalyst favoring the bonding-antibonding interactionswith the N-2 molecules. Positron annihilation studies indicatethat the electronic charge distribution within the catalyst has shallowsurface oxygen vacancies. These features in the catalyst enabled asound Faradaic efficiency of 46.4% at -0.1 V vs reversiblehydrogen electrode for the selective NH3 production inneutral electrolyte. In situ Fourier transform infrared suggests amaximum N-N bond polarization at -0.1 V and detectedH-N-H and -NH2 intermediates duringthe course of the NRR on the catalyst surface. In a broader picture,the biocompatibility of Mg2+ diversifies the utility ofthis catalyst material in N-2/biofuel cell applicationsthat would certainly offer a green alternative toward our goal ofa sustainable society. Molten saltmethod-derived monoclinic Mg2B2O5 interacts with molecular N-2 via bonding-antibondinginteractions among the energetically symmetric catalyst-reactant p-orbitalspromoting N-2 adsorption on the catalyst surface. This helpedto mitigate the competitive hydrogen evolution reaction toward a selectiveN(2) to NH3 conversion with a 46.4% Faradaic efficiency.