Elucidating the alkaline oxygen evolution reaction mechanism on platinum

Abstract

Understanding the interplay between surface chemistry, electronic structure, and reaction mechanism of the catalyst at the electrified solid/liquid interface will enable the design of more efficient materials systems for sustainable energy production. The substantial progress in operando characterization, particularly using synchrotron based X-ray spectroscopies, provides the unprecedented opportunity to uncover surface chemical and structural transformations under various (electro)chemical reaction environments. In this work, we study a polycrystalline platinum surface under oxygen evolution conditions in an alkaline electrolyte by means of ambient pressure X-ray photoelectron spectroscopy performed at the electrified solid/liquid interface. We elucidate previously inaccessible aspects of the surface chemistry and structure as a function of the applied potential, allowing us to propose a reaction mechanism for oxygen evolution on a platinum electrode in alkaline solutions.

Understanding the Oxygen Evolution Reaction Mechanism on CoOx using Operando Ambient-Pressure X-ray Photoelectron Spectroscopy

“…within the so-called pre-catalytic range. As described in a previous report (48), this is an important property, since it shows that the overpotential for generating the phase supporting highest catalytic activity is lower than that of the oxygen evolution onset. In addition, it shows that highest activity oxygen evolution occurs on Co oxides only when CoO(OH) is present on the surface.…”

“…Owing to the conformal nature of the investigated systems, as reported in our previous work (37), continuous layer stacks given by "thickness equivalents" were used to represent the catalyst structure throughout the whole investigation as a function of the applied electrochemical potential. This approach, which is similar to that used in our recent study (48,50), provides critical insights into changes of the layered catalyst structure, though quantitative thickness values must be taken as approximate and may be affected by material density and photoelectron inelastic mean free path (IMPF) differences in the different phases. Additional details of the approach can be found in the experimental section.…”

“…The obtained cyclic voltammogram (CV), measured in the APXPS setup at a scan rate of 20 mV s -1 , is reported in Figure 1b and a schematic illustration of the investigated biphasic CoO x catalyst is shown in Figure 1c. After the "dip and pull" procedure described in the methods 3 section (39,(42)(43)(44)(45)(46)48), a 19.4 ± 0.7 nm nanometer thick electrolyte layer, as determined using the inverse BeerLambert relation (39, 42-44, 46, 48), was obtained on the WE surface and provided a continuous conduction path to the bulk electrolyte. This configuration enabled study of the solid/liquid interface as a function of the applied electrochemical potential (39, 42-44, 46, 48).…”

“…Despite recent advances, nearly all in situ studies of energyrelated materials have been performed using bulk sensitive spectroscopies, such as hard X-ray XAS and XRD. The recent coupling of operational systems with surface sensitive techniques, such as X-ray photoelectron spectroscopy (XPS), provides significant opportunity for shedding new light on phenomena occurring at the solid/liquid electrified interface (38,39,40,41,42,43,44,45,46,47,48). In this work, we study, under operando conditions, the chemical and structural evolution of different conformal CoO x catalyst layers formed by plasma-enhanced atomic layer deposition (PE-ALD) on p + -Si substrates (37) as a function of the applied electrochemical potential.…”

Combined soft and hard X-ray ambient pressure photoelectron spectroscopy studies of semiconductor/electrolyte interfaces

“…By combining these two techniques, the semiconductor/aqueous electrolyte interface can be studied as it is built-up in a step-wise fashion from its initial stages of formation to an interface closely resembling that found in a functioning water splitting device. The application of AP-photoelectron spectroscopy, AP-PES, (we will use AP-PES to designate generic photoelectron spectroscopy (i.e., with soft and/or hard X-rays) under ambient conditions) for studying solid/liquid interfaces is a relatively recent development [4,5,6,7,8]. Its implementation requires novel technical solutions to minimize the elastic and inelastic scattering of electrons by the liquid phase and the relatively high pressure of gas (the vapor pressure of water at 20 °C is 17.5 Torr).…”