Effect of Free Volume Elements on the Local Dynamics of Glassy Polymers from Molecular Dynamics Simulations

Ambient conditions electrochemical production of chemicals and fuels using renewable electricity represent a low carbon and sustainable approach compared to the energy and carbon-intensive thermochemical processes. Electrochemical nitrogen reduction to ammonia (ENR) and hydrogen evolution reaction (HER) from water splitting represent promising approaches to produce ammonia and hydrogen at ambient conditions. The design of low-cost, active, and selective catalysts is essential to enable ENR and HER technologies. Transition metal nitride (TMN)-based materials have emerged as promising catalysts/catalyst support for electrochemical reactions.^1-4 Herein, we perform theoretical calculations based on density functional theory (DFT) to gain insights into reaction mechanisms, rate-limiting steps and identify descriptors of ENR and HER on TMN based materials. Our calculations show that the ENR occurs at thermodynamically favorable surface nitrogen-vacancy sites via Mars–van Krevelen mechanism. We observe a volcano-like relationship between the DFT calculated nitrogen binding energy (NBE) and the limiting potential, which suggests that the NBE can be used as a descriptor of the ENRR activity on TMN based catalysts. Several TMN candidates are predicted to show excellent activity and selectivity towards ENR. We study Pt and Pd modified TMNs as low-cost HER catalysts. Our calculations show that Pt and Pd bind strongly with TM on TMN(111) surfaces, leading to the formation of stable Pt/Pd-monolayer(ML)-TMN(111) structures. Furthermore, our calculated hydrogen binding energy demonstrates that several Pt, Pd/TMN are promising candidates for HER with a low value of limiting potential similar to that calculated on Pt(111).

References

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