Computational Study of Transition-Metal Substitutions in Rutile TiO 2 (110) for Photoelectrocatalytic Ammonia Synthesis
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Computational Study of Transition‑Metal Substitutions in Rutile TiO2 (110) for Photoelectrocatalytic Ammonia Synthesis Benjamin M. Comer1 · Max H. Lenk2 · Aradhya P. Rajanala3 · Emma L. Flynn4 · Andrew J. Medford1 Received: 19 March 2020 / Accepted: 31 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Synthesis of ammonia through photo- and electrocatalysis is a rapidly growing field. Titania-based catalysts are widely reported for photocatalytic ammonia synthesis and have also been suggested as electrocatalysts. The addition of transitionmetal dopants is one strategy for improving the performance of titania- based catalysts. In this work, we screen d-block transition- metal dopants for surface site stability and evaluate trends in their performance as the active site for the reduction of nitrogen to ammonia on TiO2. We find a linear relationship between the d-band center and metal substitution energy of the dopant site, while the binding energies of N2, N2H, and NH2 all are strongly correlated with the cohesive energies of the dopant metals. The activity of the metal-doped systems shows a volcano type relationship with the NH2 and N2H energies as descriptors. Some metals such as Co, Mo, and V are predicted to slightly improve photo- and electrocatalytic performance, but most metals inhibit the ammonia synthesis reaction. The results provide insight into the role of transition-metal dopants for promoting ammonia synthesis, and the trends are based on unexpected electronic structure factors that may have broader implications for single-atom catalysis and doped oxides. Graphic Abstract
Keywords Nitrogen fixation · Single atom catalysis · Density functional theory Benjamin M. Comer and Max H. Lenk have contributed equally to this work. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10562-020-03348-z) contains supplementary material, which is available to authorized users. Extended author information available on the last page of the article
1 Introduction The fixation of atmospheric nitrogen has long been one of the prime challenges in chemistry and chemical engineering [1, 2]. The Haber–Bosch process has been the route of choice for performing nitrogen fixation for the past century,
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permitting much of the population growth over that period [3]. However, this process has significant drawbacks, including high CO2 emissions and centralized production due to large capital requirements [4]. The Haber–Bosch process’s considerable contribution to C O2 emissions has been an increasingly pressing concern for the global community, as it accounts for 340 million tonnes of CO2—fully 2% of the carbon emissions worldwide [5, 6]. For this reason, supplanting the Haber–Bosch process would represent a significant contribution to global efforts to curb climate change. Due to the various drawbacks of the Haber–Bosch process, researchers have sought alternative means of producing fixed nitrogen [4, 7–11].
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