Abstract
The hydrogen oxidation reaction (HOR) in alkaline media is critical for the alkaline fuel cell and electrochemical ammonia compressor. The sluggishness of HOR in the alkaline electrolyte requires platinum nano-catalysts, which are scarce and expensive. Decorating Pt catalysts with transition metals can boost the area specific activity (SA) of Pt nano-catalysts, but it often reduces the electrochemical active surface area (ECSA), resulting in a limited enhancement in Pt mass activity (MA). Single-atom surface modification of Pt catalysts can significantly enhance the reaction kinetics of single molecule, but it is less effective for HOR process that involve multiple molecules, i.e. H2 and OH-. Here we use a single-atom Pd-Ru pair to boost the activity of Pt nano-catalysts without loss of surface-active sites. Using a mildly catalytic thermal pyrolysis approach, single-Pd and single-Ru atom pair are precisely decorated on Pt nanoparticle surfaces, which is confirmed by Extended X-Ray Absorption Fine Structure (EXAFS) analysis. Density functional theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations show the preferred adsorption of single-atom Pd and Ru dopants over Pd and Ru clustering on Pt surfaces. The single-atom Pd-Ru pair decorated Pt (Pd-Ru@Pt) catalyst features tri-active sites including: hydrophilic Pd promoting activation of adsorbed hydrogen atoms (Hads) via the hydrogen spill-over effect, oxyphilic Ru facilitating the adsorption of hydroxide molecules (OHads), and highly-catalytic Pt facilitating water formation with increased availability of Hads and OHads. In addition, the dopant decoration also reduces the hydrogen binding energy due to the shift of the (d) band center relative to the Fermi Level. The tri-active Pd-Ru@Pt catalyst shows 15.9 times higher area specific activity (SA) and 17.5 times larger mass activity (MA) than the state-of-the-art nano-Pt catalyst for HOR, and 2 times higher MA than nano-Pt for the hydrogen evolution reaction (HER). The mass exchange current density of single-atom Pd-Ru@Pt/C for the HOR/HER was 6.0 times that of the Pt/C, corresponding to 9.7 times that of Pd@Pt/C and 6.5 times that of Ru@Pt/C. The superior HOR/HER performance of the tri-active site catalyst is also demonstrated in ammonia and hydrogen pumps for practical application.
Coating SiO2 Support with TiO2 or ZrO2 and Effects on Structure and CO Oxidation Performance of Pt Catalysts
