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1.
J Am Chem Soc ; 2020 Dec 31.
Artigo em Inglês | MEDLINE | ID: mdl-33382947

RESUMO

The electrochemical CO2 reduction reaction (CO2RR) using Cu-based catalysts holds great potential for producing valuable multi-carbon products from renewable energy. However, the chemical and structural state of Cu catalyst surfaces during the CO2RR remains a matter of debate. Here, we show the structural evolution of the near-surface region of polycrystalline Cu electrodes under in situ conditions through a combination of grazing incidence X-ray absorption spectroscopy (GIXAS) and X-ray diffraction (GIXRD). The in situ GIXAS reveals that the surface oxide layer is fully reduced to metallic Cu before the onset potential for CO2RR, and the catalyst maintains the metallic state across the potentials relevant to the CO2RR. We also find a preferential surface reconstruction of the polycrystalline Cu surface toward (100) facets in the presence of CO2. Quantitative analysis of the reconstruction profiles reveals that the degree of reconstruction increases with increasingly negative applied potentials, and it persists when the applied potential returns to more positive values. These findings show that the surface of Cu electrocatalysts is dynamic during the CO2RR, and emphasize the importance of in situ characterization to understand the surface structure and its role in electrocatalysis.

2.
Phys Chem Chem Phys ; 21(10): 5402-5408, 2019 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-30785434

RESUMO

The rational improvement of current and developing electrochemical technologies requires atomistic understanding of electrode-electrolyte interfaces. However, examining these interfaces under operando conditions, where performance is typically evaluated and benchmarked, remains challenging, as it necessitates incorporating an operando probe during full electrochemical operation. In this study, we describe a custom electrochemical flow cell that enables near-surface-sensitive operando investigation of planar thin-film catalysts at significant hydrogen evolution reaction (HER) rates (in excess of -100 mA cm-2) using grazing incidence X-ray methods. Grazing-incidence X-ray spectroscopy and diffraction were implemented on the same sample under identical HER conditions, demonstrating how the combined measurements track changing redox chemistry and structure of Cu thin-film catalyst surfaces as a function of electrochemical conditions. The coupling of these methods with improved mass transport and hydrodynamic control establishes a new paradigm for operando measurement design, enabling unique insights into the key fundamental processes occurring at the catalyst-electrolyte interface.

3.
Nat Mater ; 14(11): 1150-5, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26366847

RESUMO

The photoelectrochemical splitting of water into hydrogen and oxygen requires a semiconductor to absorb light and generate electron-hole pairs, and a catalyst to enhance the kinetics of electron transfer between the semiconductor and solution. A crucial question is how this catalyst affects the band bending in the semiconductor, and, therefore, the photovoltage of the cell. We introduce a simple and inexpensive electrodeposition method to produce an efficient n-Si/SiOx/Co/CoOOH photoanode for the photoelectrochemical oxidation of water to oxygen. The photoanode functions as a solid-state, metal-insulator-semiconductor photovoltaic cell with spatially non-uniform barrier heights in series with a low overpotential water-splitting electrochemical cell. The barrier height is a function of the Co coverage; it increases from 0.74 eV for a thick, continuous film to 0.91 eV for a thin, inhomogeneous film that has not reached coalescence. The larger barrier height leads to a 360 mV photovoltage enhancement relative to a solid-state Schottky barrier.

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