Improvement of electrocatalysts would benefit the production of many important fuels and chemicals such as hydrogen evolution, CO2 reduction, and nitrogen reduction. Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are a class of materials that are advantageous for (photo)electrocatalysis due to their high surface area, favorable electronic transport properties, efficient light absorption, and highly tunable electronic structure. Catalysis of the nitrogen reduction reaction (NRR) (N2 + 6H+ + 6e– → 2NH3) is important to enable sustainable ammonia production for fertilizer and energy storage. Although 2D materials have shown promise for NRR, their activity and selectivity are hampered by competitive H2 generation, poor N2 solubility in aqueous media, and slow reaction kinetics. In order to engineer them for optimal performance, improved mechanistic understanding of the NRR on 2D-TMDCs is necessary. One of the strengths of TMDCs is their high tunability which allows them to be tailored for catalytic performance. In this joint experimental and theoretical work, we focus on two TMDCs that have shown promise for NRR: TiS2 and VS2 and study how to engineer better catalysts. We explore the effects of phase, defects, ligands, and transition metal on catalytic performance. Our ab initio density functional theory (DFT) calculations are performed while considering the effects of more realistic conditions of solvent and applied potential. We use a joint-DFT framework (JDFTx) that employs improved solvation models to handle solvent interfaces and grand-canonical DFT for fixed potential calculations, thereby more accurately describing the true behavior of electrochemical systems. To gain an understanding of the native material, we probe the activity and selectivity of distinct surface and edge sites with a focus on the effects of phase and intrinsic defects. We purposefully modify the density of states to understand the effects of orbital contributions to band edge states and N2 binding. With improved understanding of how tuning TMDCs can impact NRR, our goal is to guide future catalyst design and generate competitive catalysts for NRR.

Engineering two-dimensional transition metal dichalcogenide catalysts for nitrogen reduction

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