Selective photoelectrochemical (PEC) water oxidation to hydrogen peroxide is an underexplored option as opposed to the mainstream oxygen reduction reaction. Albeit interesting, selective H2O2 production via oxidative pathway is plagued by the noncontrollable two‐electron transfer reaction and the overoxidation of the thus‐formed H2O2 to O2. Here, ZnO passivator‐coated BiVO4 photoanode is reported for selective PEC H2O2 production. Both the H2O2 selectivity and production rate increase in the range of 1.0–2.0 V versus RHE under simulated sunlight irradiation. The photoelectrochemical impedance spectra and open‐circuit potentials suggest a flattened band bending and positively shifted quasi‐Fermi level of BiVO4 upon ZnO coating, facilitating H2O2 generation and suppressing the competitive reaction of O2 evolution. The ZnO overlayer also inhibits H2O2 decomposition, accelerates charge extraction from BiVO4, and serves as a hole reservoir under photoexcitation. This work offers insights into surface states and the role of the coating layer in manipulating two/four‐electron transfer for selective H2O2 synthesis from PEC water oxidation.

Hydrogen dopants and oxygen vacancies (OVs) play crucial roles in BiVO4 photoanodes. However, the decisive factor determining the charge transport of the hydrogenated BiVO4, particularly with electron small polaron formation, remains elusive. Here we show a decreased charge transport barrier upon mildly hydrogenating the nanoporous BiVO4 photoanode, as evidenced by the thermally activating photocurrent responses. Monochromatic light photoelectrochemical performance, temperature-dependent conductivity, proton nuclear magnetic resonance, and density functional theory calculation disclose that the external hydrogen atoms occupy the intrinsic OVs in the BiVO4, reducing the hopping activation energy and facilitating electron small polaron transport. The resulting BiVO4 photoanode with NiFeO x cocatalyst achieves an applied-bias photon-to-current efficiency of 1.91% at 0.58 V vs RHE with front-illumination. This study extends the common understanding of the beneficial role in conventional donor density/surface chemisorption mediations of hydrogen doping to now include small polaron hopping.

Hydrogen peroxide is an essential chemical that is attracting strong attention for energy and environmental applications. However, the struggle between the growing market demand and the unsustainability of the conventional anthraquinone method motivates the exploration of alternative H2O2 production processes. Although several new production processes have been proposed, the environmental‐friendly solar‐driven H2O2 production attracts most attention because of the only inputs of water, oxygen, and light energy. The rational design of functional photo‐responsive catalysts promotes H2O2 production in the photocatalytic and photoelectrocatalytic approaches. These are, in general, achieved by facilitating the preferential adsorption of key intermediates of OOH*/OH*/O*, enhancing the light absorption, promoting the charge separation, and accelerating the surface charge transfer with selective number of involved charges. This review systematically summarizes strategies for photo(electro)catalysts toward H2O2 production via both the water oxidation and oxygen reduction pathways. Though the oxygen reduction route is perceived as more popular in the community, selective water oxidation is emerging as a convincing alternative. Furthermore, prevailing hypotheses, state‐of‐the‐art catalysts, critical challenges, and perspectives are discussed in depth. This review aims to enhance the comprehension of this research field and promote interest in sustainable H2O2 production.

Surface engineering affects the photoelectrochemical properties of multinary oxide photoelectrodes. Here, we report a simple alkaline solution treatment of the (010) faceted bismuth vanadate (BiVO 4 ) photoanode to increase the surface ratio of bismuth to vanadium, thus improving the performance of photoelectrochemical water oxidation. This study demonstrates that the preferential vanadium dissolution occurs in an alkaline solution, resulting in a bismuth-rich surface on the outer region of the pristine BiVO 4 to afford the formation of homojunction within BiVO 4 . The homojunction promotes the charge separation efficiency of the treated BiVO 4 photoanode to reach an almost ∼100% enhancement at 1.23 V RHE under simulated sunlight. Upon further loading NiFeO x cocatalyst, the maximum applied-bias photon-to-current conversion efficiency (ABPE) of treated BiVO 4 photoanode also shows a further 100% enhancement in 0.1 M KPi electrolyte. This study sheds light on the critical role of surface termination/composition on the photoelectrochemical properties of the BiVO 4 photoanode. This essential surface property can be modulated through a simple strategy to improve its charge transport for efficient water oxidation.

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