The electrochemical nitrogen oxidation reaction (NOR) has recently drawn attention due to promising experimental and theoretical results. It provides an alternative, environmentally friendly route to directly synthesize nitrate from N 2 (g). There is to date a limited number of investigations focused on the electrochemical NOR. Herein, we present a detailed computational study on the kinetics of both the NOR and the competing oxygen evolution reaction (OER) on the TiO 2 (110) electrode under ambient conditions. The use of grand canonical density functional theory in combination with the linearized Poisson−Boltzmann equation allows a continuous tuning of the explicitly applied electrical potential. We find that the OER may either promote or suppress the NOR on TiO 2 (110) depending on reaction conditions. The detailed atomistic insights provided on the mechanisms of these competing processes make possible further developments toward a direct electrochemical NOR process.

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Density functional theory calculations are used to analyze and determine the active sites for CO 2 reduction reaction (CO 2 RR) toward CO and formic acid on TiO 2 /RuO 2 and SnO 2 /RuO 2 alloys in their rutile structure with the (110) facet. Ti and Sn atoms in TiO 2 and SnO 2 catalysts are substituted with Ru atoms with different ratios and compositions in order to determine recently observed experimental trends and gain insights into catalytic active sites. We base our analysis on constructing volcano plots in order to predict the overpotential needed for CO 2 RR on all the model systems. We observe that catalyst compositions having alternating bridge Ru−Ti as binding sites for the key intermediates of COOH or OCHO result in higher overpotentials than the reference RuO 2 surface where only H 2 is formed experimentally. If the binding sites are either bridge Ru−Ru or especially bridge Ti−Ti, it significantly lowers the overpotentials for CO formation, which indicates that these are the active sites of the TiO 2 /RuO 2 alloys. For formic acid formation, the bridge Ru−Ru sites result in the lowest overpotentials, whereas the bridge Ti−Ti sites bind the OCHO intermediate too strongly and give rise to large overpotentials. Furthermore, the calculations show clearly that when replacing Cu for one bridge Ru atom in a RuO 2 overlayer on TiO 2 , the overpotential decreases significantly toward formic acid and especially CO formation in agreement with experimental observations. Finally, for the SnO 2 /RuO 2 alloys, replacing Sn with Ru in the coordinatively unsaturated sites decreases the overpotential compared with all other model systems of the SnO 2 /RuO 2 alloys, which is due to electronic effects since the key intermediates are catalyzed on the neighboring bridge sites. The knowledge gained from these synergistic effects when manufacturing these alloys may be used to engineer the active sites for CO 2 RR in order to improve the selectivity and decrease the required overpotential.

Density functional theory is used to study the effect of varying CO coverage on selectivity and activity of CO2 reduction reaction (CO2RR) towards methanol and formic acid formation on transition...