The electrochemical reduction of N2 to NH3 (NRR) under ambient conditions is significant for sustainable agriculture. Here, by means of density functional theory (DFT) computations, the potential of a series of single transition metal (TM) atoms embedded into a MoS2 monolayer with an S-vacancy (TM/MoS2) as electrocatalysts for NRR was systematically investigated. Our DFT results revealed that among all these considered candidate catalysts, the single Mo atom embedded into the MoS2 nanosheet was found to be the most active catalyst for NRR with an onset potential of -0.53 V, in which the hydrogenation of the adsorbed N2* to N2H* is the potential-determining step. The high stabilization of the N2H* species is responsible for the superior performance of the embedded Mo atom for the NRR, which is well consistent with its d-band center. Our findings may facilitate the further design of single-atom electrocatalysts with high efficiency for NH3 synthesis at room temperature.
Searching for low-cost, efficient, and stable electrocatalysts for CO electroreduction (COER) reactions is highly desirable for the reduction of CO emission and its conversion into useful products, but remains a great challenge. In this work, single transition metal atoms supported on porphyrin-like graphene catalysts, i.e., TMN/graphene, acting as electrocatalysts for CO reduction were explored by means of comprehensive density functional theory (DFT) computations. Our results revealed that these anchored TM atoms possess high stability due to their strong hybridization with the unsaturated N atoms of the substrate and function as the active sites. On the basis of the calculated adsorption strength of COER intermediates, we have identified that single Co, Rh, and Ir atoms exhibit superior catalytic activity towards CO reduction. In particular, CHOH is the preferred product of COER on the CoN/graphene catalyst with an overpotential of 0.59 V, while the RhN/graphene and IrN/graphene catalysts prefer to reduce CO to CHO with an overpotential of 0.35 and 0.29 V, respectively. Our work may open a new avenue for the development of catalytic materials with high efficiency for CO electroreduction.
Searching for metal-free catalysts for the carbon dioxide reduction reaction (CO2RR) has been a key challenge in the electrosynthesis of fuels for CO2 utilization. In this work, we investigated the potential of N-doped graphene as the electrocatalyst of CO2RR by means of comprehensive density functional theory (DFT) computations. The computations revealed that N-doping can modify the electronic properties of graphene for enhancing the electrochemical reduction of CO2 into CO and HCOOH, resulting in a low free energy barrier for the potential-limiting step to form the key intermediate COOH as well as the strong adsorption energy of adsorbed COOH and the weak adsorption energy of CO or HCOOH. The highest catalytic activity toward CO2RR is shown by pyrrolic N-doped graphene due to its lowest overpotential of 0.24 V among all N-doped graphenes, and leads exclusively to HCOOH as the product. Therefore, our results demonstrated that N-doped graphene holds great promise as an electrocatalyst for the CO2RR with high efficiency and selectivity by suitably tuning its N species.
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