3. PHOTOELECTROCATALYTIC CO2 REDUCTION
Photoelectrochemical (PEC) CO2 reduction possesses the
advantages of both photocatalytic and electrocatalytic
CO2 reduction and has attracted a great deal of
interest.[82-84]
PEC CO2RR proceeds through the following
steps:[83]
(1) Generation of electron-hole pairs.
(2) Charge separation/transport by an external bias.
(3) Surface redox reactions:
A large amount of electron-hole recombination occurs at each stage,
releasing energy as light or heat. Therefore, the separation and
transfer of photogenerated carriers in semiconductors are key factors
for effectively improving the solar conversion efficiency.
Enormous efforts have been devoted to the design and engineering of
photocathodes, such as doping,[85-86]nanostructuring,[87-89] and co-catalyst
loading[84]. Among these, coupling a co-catalyst
with a light-absorbing semiconductor is one of the most effective
approaches for improving PEC performance. Normally, bare semiconductor
surfaces are inert and can barely activate CO2molecules, leading to poor PEC CO2RR performance. To
solve these problems, various types of co-catalysts have been loaded on
the photoelectrode to reduce the activation energy for
CO2 reduction and suppress surface charge recombination,
thus accelerating the surface reaction kinetics.