Kaijian Zhu

Photocatalytic concurrent valorization of photogenerated electrons and holes for co‐production of high‐value chemicals is an emerging strategy to maximize solar energy utilization, but its application is hindered by severe charge carrier recombination and low half‐reaction selectivity of conventional photocatalysts. Herein, we develop an asymmetric organic photocatalyst denoted as AT‐PDI, synthesized via condensation of perylene‐3,4,9,10‐tetracarboxylic dianhydride (PTCDA) with 2‐aminothiazole (2‐AT). The asymmetric molecular structure induces intrinsic electron polarization—yielding a larger dipole moment, extended electron‐hole centroid distance, and significantly enhanced built‐in electric field—which effectively facilitates charge separation and migration. Meanwhile, AT‐PDI exhibits higher 2‐electron oxygen reduction selectivity than pristine PTCDA, enabling efficient H ₂ O ₂ production via the electron‐driven half reaction, whereas photogenerated holes simultaneously oxidize benzyl alcohol to benzaldehyde. Under AM 1.5 G irradiation at pH = 2, the optimal AT‐PDI delivers H ₂ O ₂ and benzaldehyde production rates of 33.4 and 40.0 mmol·g ⁻¹ h ⁻¹ , respectively, realizing full synergistic utilization of photogenerated charge carriers. This work provides a facile asymmetric structure engineering strategy for the design of high‐performance bifunctional photocatalysts for co‐production systems.

The immobilization of a molecular electrocatalyst on gas diffusion electrodes (GDEs) overcomes mass transport limitations inherent to solution-phase CO₂ reduction.

This review extensively discusses various photoelectrode surface engineering strategies for tuning and enhancing photoelectrochemical biomass and CO ₂ valorization and provides an insightful perspective on the remaining challenges.

The performance of dye-sensitized photoelectrochemical cells is presently limited by the photocathode component. Here, we investigate the impact of nuclear dynamics on the photoinduced charge separation of the benchmark NiO/P1 system (P1 = 4-(bis-4-(5-(2,2-dicyano-vinyl)-thiophene-2-yl)-phenyl-amino)-benzoic acid). Transient absorption (TA) studies in aqueous environments with different viscosities show that photoinduced hole injection either proceeds ultrafast (<100 fs) or in a sub-ps time window. We assign the fastest component to a surface species strongly coupled to the NiO. Interestingly, the slower injection component and charge recombination are slowed down considerably in more viscous media. Quantum-classical dynamics simulations of a system with the dye standing perpendicular to the surface yield an injection lifetime remarkably close to the slow component from kinetic modeling of the TA results. Simulations including nuclear thermal motion yield a 2-fold increase in hole transfer rate compared to simulations on fixed nuclei, highlighting the role of nuclear motion and providing new design principles for dye-sensitized photocathodes.

Photocatalysis is a promising technology for purification of indoor air by oxidation of volatile organic compounds. This study provides a comprehensive analysis of the adsorption and photo‐oxidation of surface‐adsorbed acetone on three SrTiO₃ morphologies: cubes (for which exclusively {100} facets are exposed), {110}‐truncated cubes, and {100}‐truncated rhombic dodecahedrons, respectively, all prepared by hydrothermal synthesis. In situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy shows that cubic crystals contain a high quantity of surface –OH groups, enabling significant quantities of adsorbed acetone in the form of η¹‐enolate when exposed to gas phase acetone. Contrary, {110} facets exhibit fewer surface –OH groups, resulting in relatively small quantities of adsorbed η¹‐acetone, without observable quantities of enolate. Interestingly, acetate and formate signatures appear in the spectra of cubic, surface η¹‐enolate containing, SrTiO₃ upon illumination, while besides acetate and formate, the formation of (surface) formaldehyde was observed on truncated cubes, and dodecahedrons, by conversion of adsorbed η¹‐acetone. Time‐Resolved Photoluminescence studies demonstrate that the lifetimes of photogenerated charge carriers vary with crystal morphology. The shortest carrier lifetime (τ₁ = 33 ± 0.1 ps) was observed in {110}‐truncated cube SrTiO₃, likely due to a relatively strong built‐in electric field promoting electron transport to {100} facets and hole transport to {110} facets. The second lifetime (τ₂ = 259 ± 1 ps) was also the shortest for this morphology, possibly due to a higher amount of surface trap states. Our results demonstrate that SrTiO₃ crystal morphology can be tuned to optimize performance in photocatalytic oxidation.

The donor–acceptor (D–A) dye 4‐(bis‐4‐(5‐(2,2‐dicyano‐vinyl)‐thiophene‐2‐yl)‐phenyl‐amino)‐benzoic acid (P1) has been frequently used to functionalize NiO photocathodes and induce photoelectrochemical reduction of protons when coupled to a suitable catalyst. Photoinduced twisting of the P1 dye is steered on NiO by co‐adsorption of tetradecanoic acid (C₁₄, myristic acid (MA)). Density Functional Theory and time‐resolved photoluminescence studies confirm that twisting lowers the energy levels of the photoexcited D–A dye. The apolar environment provided by the MA suppresses photoinduced D–A twisting, retards charge recombination following photoinduced charge separation between P1 and NiO, and provides a larger electrochemical potential increasing the photocurrent. Very interestingly, co‐adsorption of MA induces H₂ evolution upon photoexcitation without the presence of an H₂ evolution catalyst. Based on prior art, the formation of H₂ is assigned to the dissolution of Ni²⁺, followed by reduction and re‐deposition of Ni nanoparticles acting as the catalytically active site. It propose that only excited P1 with suppressed twisting provides the sufficient electrochemical potential to induce deposition of Ni nanoparticles. The work illustrates the importance of understanding the effects of photoinduced intramolecular twisting and highlights the promise of designing twisting‐limited D–A dyes to create efficient solar fuel devices.

NiO electrodes are widely applied in p-type dye-sensitized solar cells (DSSCs) and photoelectrochemical cells, but due to excessive charge recombination, the efficiencies of these devices are still too low for commercial applications. To understand which factors induce charge recombination, we studied electrodes with a varying number of NiO layers in benchmark P1 p-DSSCs. We obtained the most efficient DSSCs with four layers of NiO (0.134%), and further insights into this optimum were obtained via dye loading studies and in operando photoelectrochemical immittance spectroscopy. These results revealed that more NiO layers led to an increasing light harvesting efficiency (η_LH), but a decreasing hole collection efficiency (η_CC), giving rise to the maximum efficiency at four NiO layers. The decreasing η_CC with more NiO layers is caused by longer hole collection times, which ultimately limits the overall efficiency. Notably, the recombination rates were independent of the number of NiO layers, and similar to those observed in the more efficient n-type DSSC analogues, but hole collection was an order of magnitude slower. Therefore, with more NiO layers, the beneficial increase in η_LH can no longer counteract the decrease in η_CC due to slow hole collection, resulting in the overall efficiency of the solar cells to maximize at four NiO layers.

Dye-sensitized photocathodes attract wide interest because of their ease of fabrication and tunability in properties for light-driven proton or CO2 reduction. They are often based on nanocrystalline NiO, functionalized with a photosensitizer and catalyst, immersed into an aqueous electrolyte optionally saturated with CO2. Developing fundamental insight into their photo- and structural dynamics, especially as a function of the nanostructure and process conditions to which the photocathode is exposed, is essential to realize efficient design approaches. The present work reviews research progress over the last two decades, including (i) the design of an impressive variety in NiO nanostructures, photosensitizers, catalysts, and combined assemblies and (ii) the present mechanistic understanding. We highlight the importance of time-resolved spectroscopy studies under operating conditions to associate the early-time photodynamical processes with the overall photocatalytic performance and to understand the effects of surface-adsorbed species on the photodynamics. The nature and concentration of the ions in the electrolyte can play a major role in steering light-induced charge separation and recombination dynamics. We also discuss the importance of developing a better understanding of the interplay between the structural dynamics and the photoinduced charge and proton transfer dynamics to improve the photocathode performance and present several research perspectives.