Searching for an alternative nonhazardous catalyst for direct urea synthesis that avoids the traditional route of NH 3 synthesis followed by CO 2 addition is a challenging field of research nowadays. Based on first-principles calculations, we herein propose a novel electrocatalyst comprising of totally nonmetal earth abundant elements (dual-Si doped g-C 6 N 6 sheet) which is capable of activating N 2 and making it susceptible toward direct insertion of CO into the N−N bond, producing *NCON* which is the precursor for urea production by direct coupling of N 2 and CO 2 followed by multiple proton coupled electron transfer processes. Remarkably, the calculated onset potential for urea production is much less than that of NH 3 synthesis and hydrogen evolution reactions, and also the faradaic efficiency is nearly 100% for production urea over ammonia, which promotes exclusive electrocatalytic urea synthesis by suppressing the NH 3 synthesis as well as hydrogen evolution reactions.
Designing metal-free photocatalysts for oxygen reduction reaction (ORR) is an important step toward the development of sustainable and alternative energy resources because ORR plays a key role in fuel cell reactions. An efficient photocatalyst for ORR must possess suitable band positions with respect to electrochemical potentials of ORR, minimize energy losses due to charge transport and electron−hole recombination, and have kinetically suitable electron transfer properties. Using first-principles theoretical studies, we herein demonstrate that a single Si atom doped on the alternative pores of the porous graphitic carbon nitride (g-C 6 N 6 ) surface has satisfied the above criteria and has the potential to be an efficient photocatalyst for ORR. Our study reveals that molecular oxygen, chemisorbed on the dopant atom of the doped surface via an end-on fashion, is activated and readily reduced with a very low onset potential (−0.07 V) via a fourelectron transfer pathway. Thus, the doped system can act as an efficient metal-free photocathode in fuel cells.
Fixation of dinitrogen into ammonia is an essential biological process for the evolution of life, and at the same time ammonia is an essential component for many industrial processes, including fertilizers, plastics, and so on. NH 3 is also known as the best alternative to H 2 in fuel cells. However, due to chemical inertness, direct conversion of N 2 into NH 3 is not possible; a suitable catalyst is required. The century-old Haber−Bosch process, utilizing an Fe-based catalyst, is extremely energy-intensive and eco-unfriendly due to the consumption of fossil fuels. In recent years, huge development has taken place in the design and applications of suitable electro-and photocatalysts for artificial N 2 fixation. First-principles calculations have been considered as a powerful avenue for theoretical screening of promising catalysts through rational design and analysis of the plausible mechanisms or pathways of reactions. The present review focuses on recent theoretical developments of various unsupported nanoclusters and supported single-atom and cluster catalysts for application in electro-and photochemical N 2 reduction reactions. The support substrates include oxides, carbides, nitrides of metal-based 2D materials, porous carbonaceous materials, and metal-free 2D materials containing main-group elements like B, C, N, and P. Although some reviews have already been made, focusing on the research related to either electro-or photocatalytic N 2 fixation on different catalysts, here we give a comprehensive account of both electrochemical and photochemical nitrogen reduction reaction (NRR) activities and selectivities of various supported single-atom and polyatomic cluster catalysts. Additionally, a comparative assessment is made on the basis of free energy of adsorption, most favorable pathway, potential limiting step, and corresponding limiting potential of the NRR.
The reverse water gas shift (RWGS, CO formation) and formic acid (FA) production are two main reaction pathways during the initial hydrogenation stages of CO2 methanation. Here, we predict that...
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