Molybdenum sulfide (MoS₂) is the most widely studied transition-metal dichalcogenide (TMDs) and phase engineering can markedly improve its electrocatalytic activity. However, the selectivity toward desired products remains poorly explored, limiting its application in complex chemical reactions. Here we report how phase engineering of MoS₂ significantly improves the selectivity for nitrite reduction to nitrous oxide, a critical process in biological denitrification, using continuous-wave and pulsed electron paramagnetic resonance spectroscopy. We reveal that metallic 1T-MoS₂ has a protonation site with a pK_a of ∼5.5, where the proton is located ∼3.26 Å from redox-active Mo site. This protonation site is unique to 1T-MoS₂ and induces sequential proton−electron transfer which inhibits ammonium formation while promoting nitrous oxide production, as confirmed by the pH-dependent selectivity and deuterium kinetic isotope effect. This is atomic-scale evidence of phase-dependent selectivity on MoS₂, expanding the application of TMDs to selective electrocatalysis.

硫化钼（MoS ₂）是研究最广泛的过渡金属二卤化二硫（TMDs），相工程可以显着提高其电催化活性。但是，对所需产物的选择性仍未得到很好的探索，限制了其在复杂化学反应中的应用。在这里，我们报道了使用连续波和脉冲电子顺磁共振波谱，MoS _2的相工程如何显着提高亚硝酸盐还原成一氧化二氮的选择性，这是生物反硝化的关键过程。我们发现金属1T-MoS ₂的质子化点的ap K _a为〜5.5，质子位于氧化还原活性的Mo处〜3.26Å。该质子化位点是1T-MoS特有的₂和诱导顺序质子电子转移，抑制铵的形成，同时促进一氧化二氮的产生，如pH依赖的选择性和氘动力学同位素效应所证实。这是对MoS ₂的相依选择性的原子尺度证据，从而将TMDs应用于选择性电催化。