We address the low selectivity problem faced by the electrochemical nitrogen (N2) reduction reaction (NRR) to ammonia (NH3) by exploiting the Mars-van Krevelen (MvK) mechanism on two-dimensional (2D) Ti2N nitride MXene. NRR technology is a viable alternative to reducing the energy and greenhouse gas emission footprint from NH3 production. Most NRR catalysts operate by using an associative or dissociative mechanism, during which the NRR competes with the hydrogen evolution reaction (HER), resulting in low selectivity. The MvK mechanism reduces this competition by eliminating the adsorption and dissociation processes at the sites for NH3 synthesis. We show that the new class of 2D materials, nitride MXenes, evoke the MvK mechanism to achieve the highest Faradaic efficiency (FE) towards NH3 reported for any pristine transition metal-based catalyst—19.85% with a yield of 11.33 μg/cm2/hr at an applied potential of − 250 mV versus RHE. These results can be expanded to a broad class of systems evoking the MvK mechanism and constitute the foundation of NRR technology based on MXenes.

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Carbon dioxide (CO 2 ) is one of the main causes of global warming, with the burning of fossil fuels being the main source of anthropogenic CO 2 . For this reason, the capture and reduction of CO 2 to value-added chemicals powered by renewable energy sources is on the forefront of electrocatalyst and photocatalyst research. The choice of catalyst, support structure, and electrolyte are the main factors that impact the electrochemical CO 2 reduction reaction (CO 2 RR) to value-added chemicals and fuels. Therefore, an understanding of each of these factors must be gained prior to large-scale applications. In this review, we provide an overview on the field of CO 2 RR electrocatalysis based on nonprecious transition metal based catalysts with a focus on their design, synthesis, characterization, and mechanisms of CO 2 RR. Special attention is paid to advanced catalysts design incorporating two-dimensional (2D) transition metal carbide and nitride materials, and state-of-the-art in situ/operando spectroelectrochemical techniques. Lastly, remaining grand challenges in the field and outlooks for future research and opportunities are provided.

MXenes have shown great promise as electrocatalysts for the hydrogen evolution reaction (HER), but their mechanism is still poorly understood. Currently, the benchmark Ti3C2 MXene suffers from a large overpotential....

The oxygen reduction reaction (ORR) is a critical but sluggish reaction used for various applications, including fuel cells and metal-oxygen batteries. Currently, the benchmark catalysts for ORR are Pt-based catalysts. However, due to these catalysts being scarce and very expensive, alternative catalysts that are more abundant and less expensive are urgently in demand. MXenes, a new two-dimensional (2D) material based on transition metal carbides and nitrides, have advanced the performance of various existing applications and technologies, including batteries, supercapacitors, sensors, etc. Owing to their unique electronic structure, physical and chemical properties, and tunable morphology, MXenes are expected to thrive as catalysts in ORR electro- and photo-catalytic systems. Additionally, they are promising catalytic supports for ORR, thus significantly reducing the necessary Pt loading. In this work, we carefully review the most pertinent works on ORR using MXenes. We discuss the gaps and challenges in the field, identify key areas that need further attention, and provide directions for future research.