Tuning Product Selectivity in Direct Electroreduction of NO via Phase Engineering of MoS2 Nanosheets in Water-fed PEM Electrolyzer

Abstract

Converting the NO from gaseous pollutants into ammonia through electro-reduction using abundant and cost-effective catalyst materials holds great promise for pollutant abatement and towards a more-closed, sustainable nitrogen cycle. However, regulating reaction selectivity has proven to be a challenge, due to the difficulty in controlling complex multielectron/proton reactions. Here, we report two different crystal phases MoS₂ (2H and 1T') exhibiting prominent activity in electrocatalytic NO reduction. The faradaic efficiency of ammonia reaches 86% over 2H-MoS₂, outperforming that of 1T'-MoS₂ (31%) at 2.1 V. Interestingly, the phase affects the product selectivity -1T'-MoS₂ displays higher selectivity towards N₂, especially at lower cell voltage (50% at 1.7 V). XPS results indicate that 1T'-MoS₂ forms distorted Mo(V) oxo species intermediate that induces sequential proton-electron transfer and promotes N-N bond formation. In contrast, over 2H-MoS₂, ammonia production is promoted through the centered proton-electron transfer. Overall, the electrochemical NORR can be efficiently performed with good selectivity by the appropriate choice of MoS₂ phase.