Operando Raman spectroscopy tracks oxidation-state changes in an amorphous Co oxide material for electrocatalysis of the oxygen evolution reaction

Abstract

How cations affect the electric double layer and the rates and selectivity of electrocatalytic processes

Modifying redox properties and local bonding of Co3O4 by CeO2 enhances oxygen evolution catalysis in acid

“…The intensities of all Raman peaks at higher applied potentials decrease substantially (Fig. 5b, c lower panel), which was usually accompanied with the increase in average valence state of Co atoms 63 . When the applied potential was finally switched back from 1.87 to 1.22 V vs. RHE, the peak intensities partially recovered (lower panel in Fig.…”

“…Co 3 O 4 /CeO 2 showed a red-shift in the A 1g peak position after the onset of OER at 1.52 V vs. RHE. Red-shifts in Raman signals are commonly observed in OER catalysts (CoO x 63 , 66 , NiOOH 67 , NiFe, and CoFe oxyhydroxides 68 ) at OER operating potentials, and they generally reflect the characteristic vibration for local bonding environment at the outer layer of catalysts with oxidized active site during OER. Thus, the generation of active Co IV species that can participate in a fast and efficient OER process should lead to the observed red-shift of the Raman signals.…”

Boosting Surface Reconstruction for the Oxygen Evolution Reaction: A Combined Effect of Heteroatom Incorporation and Anion Etching in Cobalt Silicate Precatalyst

“…The OER process comprises the Co species to undergo a redox transition of Co 2+ /Co 3+ and Co 3+ /Co 4+ where the higher oxidation Co species is generally considered the active site. The above transformation requires significant energy and lowering this energy is known to improve the catalytic activity [9–11] . Incorporation of metallic (Fe/Cr/W/Mo/Pb) and/or non‐metallic elements (S/P/B/N) have been known to improve the OER output for Co based electrocatalyst [12–20] .…”

“…The above transformation requires significant energy and lowering this energy is known to improve the catalytic activity. [9][10][11] Incorporation of metallic (Fe/Cr/W/Mo/Pb) and/or non-metallic elements (S/P/B/N) have been known to improve the OER output for Co based electrocatalyst. [12][13][14][15][16][17][18][19][20] Recently, several research groups have pointed out that often the as-synthesized catalysts are regarded as precatalyst, which undergoes surface transformation to generate the real catalyst, also referred as the active catalyst.…”

Quantification of Redox Sites during Catalytic Propane Oxychlorination by Operando EPR Spectroscopy

“…Significant advances have been made in electro‐ and homogeneous catalysis in the liquid phase, enabling to relate performance and oxidation state [8] . Yet, efforts in the field of heterogeneously‐catalyzed gas‐phase reactions have been mainly limited to establishing correlations with spectral features, such as white line intensity of XAS signals or integral of EPR spectra, thus only allowing for semi‐quantitative analyses [3a, 5a, 6b, 7d] . This is primarily due to the need for using comparatively high temperatures, pressures, and/or highly‐reactive species (e.g., O 2 , H 2 , NH 3 , halogens) in order to activate light hydrocarbons.…”