This review describes the current understanding of CO2 photoreduction on the surface of heterogeneous catalysts with a particular focus on the reaction mechanism and pathways as well as the adsorption/activation of CO2.
Surface reaction kinetics and bulk charge separation are both critical to the efficiency of solar water splitting. In addition to the well-documented surface catalytic effect, the promotion of bulk charge separation upon loading of cocatalysts has rarely been reported. This paper describes the synergetic enhancement of surface reaction kinetics and bulk charge separation by introducing discrete nanoisland p-type Co3O4 cocatalysts onto n-type BiVO4, forming a p-n Co3O4/BiVO4 heterojunction with an internal electric field to facilitate charge transport. Being highly dispersed on the surface of photoanodes, the nanoisland cocatalysts could suppress the formation of recombination centers at the photoanode/cocatalyst interface. This cocatalyst-loading method achieved a charge separation efficiency of up to 77% in the bulk and 47% on the surface of catalysts. An AM 1.5G photocurrent of 2.71 mA/cm(2) at 1.23 V versus the reversible hydrogen electrode for water oxidation was obtained, which is the highest photocurrent yet reported for Co-catalyzed undoped BiVO4 photoanodes, with a photoconversion efficiency of 0.659%.
Cu-catalyzed selective electrocatalytic
upgrading of carbon dioxide/monoxide
to valuable multicarbon oxygenates and hydrocarbons is an attractive
strategy for combating climate change. Despite recent research on
Cu-based catalysts for the CO2 and CO reduction reactions,
surface speciation of the various types of Cu surfaces under reaction
conditions remains a topic of discussion. Herein, in situ surface-enhanced
Raman spectroscopy (SERS) is employed to investigate the speciation
of four commonly used Cu surfaces, i.e., Cu foil, Cu micro/nanoparticles,
electrochemically deposited Cu film, and oxide-derived Cu, at potentials
relevant to the CO reduction reaction in an alkaline electrolyte.
Multiple oxide and hydroxide species exist on all Cu surfaces at negative
potentials, however, the speciation on the Cu foil is distinct from
that on micro/nanostructured Cu. The surface speciation is demonstrated
to correlate with the initial degree of oxidation of the Cu surface
prior to the exposure to negative potentials. Combining reactivity
and spectroscopic results on these four types of Cu surfaces, we conclude
that the oxygen containing surface species identified by Raman spectroscopy
are unlikely to be active in facilitating the formation of C2+ oxygenates in the CO reduction reaction.
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