Nitric Oxide (NO) electroreduction is highly important in the environmental, industrial, and biological sectors. Adsorbed NO is an intermediate that is considered to be a selectivity-determining species during many electrochemical reactions; for example, in electrochemical denitrification, NO is considered the key intermediate step leading to the removal of toxic nitrate and nitrite species from groundwater. Though NO is thought to be a key step in the determining the selectivity of products in NOx reduction, minimal studies have addressed the precise atomistic details about the potential-dependent mechanism for NO electroreduction. In this work, we employ a multiscale computational approach to gain insight into the reaction pathway for NO reduction on the Pt(100) surface. Using periodic, self-consistent DFT calculations, we illustrate the thermodynamics and kinetics of a series of intermediates for the electrochemical conversion of NO to ammonia (NH4+), nitrogen gas (N2), and nitrous oxide (N2O) at both low and saturated NO coverages. Our results illustrate that contrary to the Pt(111) surface, the dissociation of the N-O bond is accessible through the HNO intermediate on the 100 surface. However, based upon density functional theory results, we find that there is a significant kinetic competition between HNO and NOH intermediates at low coverage, while at experimentally observed NO coverages (ca. 0.45 ML) there is a significant thermodynamic and kinetic competition between intermediates leading to the formation of NH4+. By employing kinetic Monte Carlo simulations, however, we not only take into account coverage-dependence and time, but also simulate experimental conditions (i.e., voltage sweep over time) and shed light on the electrochemical reduction reaction. Ultimately, we not only show a direct one-to-one comparison to voltammetric sweep data obtained in previous experimental reports, but also identify the essential intermediates and mechanism for NO reduction at experimentally observed potentials. In addition, our approach solves the mystery of why, though thermodynamically preferred, N2 (g) (as well as N2O (g)) is not produced in the electrochemical reduction of NO on the Pt(100) surface in acidic conditions.

Electrochemical reduction of nitric oxide on Pt-surfaces: A combined DFT and kMC approach

253rd National Meeting (2017)

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