The origins of the pH-dependent kinetics of hydrogen evolution and oxidation reactions on Pt surfaces are unsolved dilemmas that have lasted for over half a century. In this study, surface-enhanced infrared absorption spectroscopy is applied to directly monitor the vibrational behaviors of adsorbed hydrogen atoms and interfacial water molecules on Pt surfaces in a wide pH window from 1.1 to 12.9. For the first time, we successfully measure the pH-dependent changes of hydrogen and water binding strength according to their vibrational wavenumbers, which are both monotonously weakened as the solution pH increases. Their changes are the net results of altered electrochemical interface environments and are important contributions to the pH-dependent hydrogen reaction kinetics. Our results add significant new insights into the role of interfacial environments on electrocatalysis.
With the rapid development of fuel cell technology, the low reduction rate of oxygen on Pt-based cathodes is generally considered the main obstacle. Pt/transition metal alloys (Pt–Ms) or Pt/transition metal oxides (Pt–MOx) can be formed by doping transition metal atoms into the lattice of the Pt layer or depositing onto the surface of the Pt layer to intensify the catalytic activity of the electrodes. In this work, a stepwise solution chemical reduction method for high dispersion of cobalt oxyhydroxide (–OCoOH) deposited onto the facet of Pt as nano-islands and the mechanism of promoting the oxygen reduction reaction (ORR) at the cathode have been investigated by density functional theory (DFT) calculation. As a result, the electrocatalytic activity of Pt with nano-island –OCoOH structure was 3.6 times that of the Pt/C catalyst, which indicated that promoting the desorption of the first O atom and weakening the adsorption capacity of the interfacial junction Pt for the second O atom from adsorbed oxygen attributed to the migration of d-band center in Pt and the existence of the Co hydroxyl group.
Water electro-oxidation to form H 2 O 2 is an important way to produce H 2 O 2 which is widely applied in industry. However, its mechanism is under debate and HO (ads) , hydroxyl group adsorbed onto the surface of the electrode, is regarded as an important intermediate. Herein, we study the mechanism of water oxidation to H 2 O 2 at Pt electrode using in-situ Raman spectroscopy and differential electrochemical mass spectroscopy and find peroxide bond mainly originated from the coupling of two CO 3 2- via a C 2 O 6 2- intermediate. By quantifying the 18 O isotope in the product, we find that 93% of H 2 O 2 was formed via the CO 3 2- coupling route and 7% of H 2 O 2 is from OH (ads) -CO 3 •− route. The OH (ads) -OH (ads) coupling route has a negligible contribution. The comparison of various electrodes shows that the strong adsorption of CO 3(ads) at the electrode surface is essential. Combining with a commercial cathode catalyst to produce H 2 O 2 during oxygen reduction, we assemble a flow cell in which the cathode and anode simultaneously produce H 2 O 2 . It shows a Faradaic efficiency of 150% of H 2 O 2 at 1 A cm −2 with a cell voltage of 2.3 V.
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