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Surface Chemistry and Catalysis From First Principles

  • Author(s): Hu, Guoxiang
  • Advisor(s): Jiang, De-en
  • et al.
Abstract

Hydrogen-catalyst interaction is the foundation of many technologies and processes. Herein we employ first principles density functional theory (DFT) techniques to investigate how hydrogen interacts with different catalytic systems, including cobalt phosphide (CoP), h-BN monolayer supported on transition metals (h-BN/metal), atomically precise gold nanoclusters, and titanium dioxide (TiO2). Our study has important implications for the use of the catalysts for hydrogen evolution reaction (HER), CO2 reduction, and H2 activation.

Electrochemical HER using renewable energy can provide a sustainable supply of fuel for future societies with hydrogen as a key energy carrier. CoP is one of the most active earth-abundant electrocatalysts for HER. We have studied the adsorption structures and energetics of atomic hydrogen on several low-Miller-index surfaces of CoP. We find that CoP(111) is the most promising facet for high and long-lived HER activity. Compared to HER, CO2 reduction is much harder. Since HER competes with CO2 reduction at all negative potentials, a key criterion for selective catalysts in CO2 reduction is the avoidance of HER. We have investigated the electrocatalytic activities of h-BN/Ni, h-BN/Co, and h-BN/Cu. We find that the competitive HER channel can be filtered out by the surface h-BN monolayer for h-BN/Ni and h-BN/Co, making them very good electrocatalysts for CO2 reduction.

Atomically precise gold nanoclusters are a new class of catalysts, and it is able to establish structure-activity correlations due to their well-defined structures. Thiolate-protected gold nanoclusters have received considerable research attention, and have been reported to exhibit high HER activity. We have studied the thiolate-gold interface and find that the interfacial structures of thiolates on gold are surface sensitive. To understand HER on the thiolate-protected gold nanoclusters, we have studied how hydrogen interacts with [Au25(SR)18]q clusters (q=-1, 0, +1) and monoatom-doped bimetallic [M1Au24(SR)18]q clusters (M=Pt, Pd, Ag, Cu, Hg, Cd, and q=-2, -1, 0). We conclude that PtAu24(SR)18, PdAu24(SR)18, and CuAu24(SR)18 clusters can be very good electrocatalysts for HER. Unlike the above thiolate-protected gold nanoclusters, where the surface gold atoms are fully coordinated by the thiolates, the Au22(L8)6 cluster (L = 1,8-bis(diphenylphosphino) octane) is unique in that it contains eight coordinatively unsaturated (cus) gold atoms. We find that the eight cus gold atoms in the Au22(L8)6 cluster can adsorb hydrogen stronger than Pt, thereby being a potentially promising catalyst for HER.

Hydrogen interaction with metal oxides is of growing interest recently. TiO2 is one of the most extensively investigated metal oxides. We have studied the mechanisms of H2 activation on the surfaces of different TiO2 polymorphs, including rutile TiO2(110), anatse TiO2(101), and brookite TiO2(210). We find that for all the three surfaces, although the homolytic dissociation of H2 is thermodynamically more favorable, the heterolytic pathway is kinetically more favorable.

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