High-throughput synthesis and screening of binary alloys for hydrogen evolution and oxidation reactions

Description/Abstract

High throughput methods were employed for the physical vapour deposition (PVD) and electrochemical screening of random and equilibrated (annealed at 300 ºC for 15 minutes) binary metal alloys for the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR). Results are presented for the Pd-Au, Pd-Bi and Ru-Au alloy systems. Thin films of each alloy system were synthesized on a series of 10x10 array electrodes with a graded composition. A variety of analytical techniques including Energy Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and powder X-ray Diffraction (XRD) were used for the analysis of bulk composition, surface composition and structure respectively. The compositional analysis reveals that alloy formation and synthesis of nearly the whole compositional range of the alloy systems were achieved. Surface segregation of Au in the Pd-Au alloy system and Ru in the Ru-Au alloy system was observed. The surface segregation in the equilibrated Pd-Bi alloy system did not take place. The HER and HOR activity on all the examined alloy systems exhibit a similar compositional dependence. This suggests that the HER activity provides a good descriptor for the HOR activity for systems with low overpotentials. An exception of this occurs, however, at high concentrations of Au and Bi where the HER activity decreases monotonically towards 100 at. %, while the HOR activity decreases more rapidly at alloy compositions of ca. 90 at. %. An enhancement in the activity was found on a variety of alloy compositions over the constituent components. The optimum Pd-Au alloy composition for the HER and HOR was found to be at a composition of ca. Pd50Au50 (more active than pure Pd). A comparable activity to pure Pd was found on Birich alloys (ca. Pd25Bi75) in the Pd-Bi alloy system. The activity on ca. Ru90Au10 and 60-80 % Au was found to be higher than pure Ru. The CO-tolerance in the HOR along the whole compositional range of each alloy system was also assessed in the presence of a mixture of hydrogen and 500 ppm CO. The results suggest that the Ru-Au alloy system is more CO tolerant than the other two systems