Embedding Nano-Piezoelectrics into Heterointerfaces of S-Scheme Heterojunctions for Boosting Photocatalysis and Piezophotocatalysis

Step-scheme (S-scheme) heterojunctions have exhibited great potential in photocatalysis due to their extraordinary light harvesting and high redox capacities. However, inadequate S-scheme recombination of useless carriers in weak redox abilities increases the probability of their recombination with useful ones in strong redox capabilities. Herein, a versatile protocol is demonstrated to overcome this impediment based on the insertion of nano-piezoelectrics into the heterointerfaces of S-scheme heterojunctions. Under light excitation, the piezoelectric inserter promotes interfacial charge transfer and produces additional photocarriers to recombine with useless electrons and holes, ensuring a more thorough separation of powerful ones for CO2 reduction and H2 O oxidation. When introducing extra ultrasonic vibration, a piezoelectric polarization field is established, which allows efficient separation of charges generated by the embedded piezoelectrics and expedites their recombination with weak carriers, further increasing the number of strong ones participating in the redox reactions. Encouraged by the greatly improved charge utilization, significantly enhanced photocatalytic and piezophotocatalytic activities in CH4 , CO, and O2 production are achieved by the designed stacked catalyst. This work highlights the importance in strengthening the necessary charge recombination in S-scheme heterojunctions and presents an efficient and novel strategy to synergize photocatalysis and piezocatalysis for renewable fuels and value-added chemicals production.

Synergy of Surface Phosphates and Oxygen Vacancies Enables Efficient Photocatalytic Methane Conversion at Room Temperature

Room-temperature photocatalytic conversion of CH₄ into liquid oxygenates with O₂/H₂O provides an appealing route for sustainable chemical industry, which, however, suffers from poor efficiency due to the undesired carrier kinetics and low yield of reactive oxygen species of the currently available photocatalysts. Here, we report an effective surface engineering strategy where concurrent constructions of oxygen vacancies and phosphate sites on TiO₂ nanosheets address the above challenge. The surface oxygen vacancies and phosphates are respective acceptors of photogenerated electrons and holes for promoted separation and migration of charge carriers. Moreover, in addition to the facilitated activation of O₂ to ^•OH by electrons at oxygen vacancies, the surface phosphates also facilely adsorb H₂O via hydrogen bonds and thus effectively transfer holes to H₂O for enhanced ^•OH production, thereby boosting CH₄ conversion. As a result, compared with TiO₂ sheets with only oxygen vacancies, a 2.8 times improvement in liquid oxygenate production with near-unity selectivity is achieved by virtue of the synergy of surface oxygen vacancies and phosphate sites, together with an unprecedent quantum efficiency of 19.8% under 365 nm irradiation.

Overall Photocatalytic CO2 Reduction over Heterogeneous Semiconductor Photocatalysts

The overall photocatalytic CO2 reduction reaction (PCRR), which uses solar energy to convert CO2 and H2O into chemical feedstocks or fuels without sacrificial reagents, plays a momentous role in CO2 utilization and solar energy conversion. However, significant challenges remain in achieving efficient conversion. Researchers have explored various strategies to realize the overall PCRR efficiently. In this review, we first explain the criteria for evaluating the overall PCRR and then summarize the following strategies developed over the past decade to promote it: self-driving material development, Z-scheme heterojunction construction, cocatalyst loading, heteroatom doping, surface vacancy creation, and carrier-material matching. Finally, we discuss essential future research directions in the field. Through this comprehensive review, we aim to provide strategic guidance for the development of efficient overall PCRR systems.

Tailored BiVO4 Photoanode Hydrophobic Microenvironment Enables Water Oxidative H2 O2 Accumulation

Direct photoelectrochemical 2-electron water oxidation to renewable H₂ O₂ production on an anode increases the value of solar water splitting. BiVO₄ has a theoretical thermodynamic activity trend toward highly selective water oxidation H₂ O₂ formation, but the challenges of competing 4-electron O₂ evolution and H₂ O₂ decomposition reaction need to overcome. The influence of surface microenvironment has never been considered as a possible activity loss factor in the BiVO₄ -based system. Herein, it is theoretically and experimentally demonstrated that the situ confined O₂ , where coating BiVO₄ with hydrophobic polymers, can regulate the thermodynamic activity aiming for water oxidation H₂ O₂ . Also, the hydrophobicity is responsible for the H₂ O₂ production and decomposition process kinetically. Therefore, after the addition of hydrophobic polytetrafluoroethylene on BiVO₄ surface, it achieves an average Faradaic efficiency (FE) of 81.6% in a wide applied bias region (0.6-2.1 V vs RHE) with the best FE of 85%, which is 4-time higher than BiVO₄ photoanode. The accumulated H₂ O₂ concentration can reach 150 µm at 1.23 V versus RHE under AM 1.5 illumination in 2 h. This concept of modifying the catalyst surface microenvironment via stable polymers provides a new approach to tune the multiple-electrons competitive reactions in aqueous solution.

Spatially Separated Redox Cocatalysts on Ferroelectric Nanoplates for Improved Piezophotocatalytic CO2 Reduction and H2O Oxidation

Utilizing solar and mechanical vibration energy for catalytic CO₂ reduction and H₂O oxidation is emerging as a promising way to simultaneously generate renewable energy and mitigate climate change, making it possible to integrate two energy resources into a reaction system for artificial piezophotosynthesis. However, the practical applications are hindered by undesirable charge recombination and sluggish surface reaction in the photocatalytic and piezocatalytic processes. This study proposes a dual cocatalyst strategy to overcome these obstacles and improve the piezophotocatalytic performance of ferroelectrics in overall redox reactions. With the photodeposition of AuCu reduction and MnO_x oxidation cocatalysts on oppositely poled facets of PbTiO₃ nanoplates, band bending occurs along with the formation of built-in electric fields on the semiconductor-cocatalyst interfaces, which, together with an intrinsic ferroelectric field, piezoelectric polarization field, and band tilting in the bulk of PbTiO₃, provide strong driving forces for the directional drift of piezo- and photogenerated electrons and holes toward AuCu and MnO_x, respectively. Besides, AuCu and MnO_x enrich the active sites for surface reactions, significantly reducing the rate-determining barrier for CO₂-to-CO and H₂O-to-O₂ transformation, respectively. Benefiting from these features, AuCu/PbTiO₃/MnO_x delivers remarkably improved charge separation efficiencies and significantly enhanced piezophotocatalytic activities in CO and O₂ generation. This strategy opens a door for the better coupling of photocatalysis and piezocatalysis to promote the conversion of CO₂ with H₂O.