Water Oxidation Kinetics Research Articles

Schiff Base Complex Cocatalyst with Coordinatively Unsaturated Cobalt Sites for Photoelectrochemical Water Oxidation.

Integrating inorganic oxygen evolution cocatalysts (OECs) with photoanodes is regarded as an available strategy to increase the photogenerated charge utilization for accelerated water oxidation kinetics. Nevertheless, most widely used transition metal (oxyhydr)oxides OECs suffer from inevitable charge recombination at photoanode/OECs interfaces and underabundant catalytic active sites. Herein, a cobalt-organic complex with microflower-like features (denoted as MF) was constructed by coordination of Schiff base ligands and Co2+ metal ions and then decorated on porous BiVO4 employed as photoanodes for photoelectrochemical (PEC) water oxidation. The as-synthesized BiVO4/MF photoanode achieves a photocurrent density of 4.38 mA cm-2 and at 1.23 VRHE in 0.5 M Na2SO4 electrolyte under simulated 1 sun illumination, over approximately 5.48 times larger than that of BiVO4 counterpart, and exhibits a 120 mV cathodic shift of onset potential with outstanding photostability. Systematic characterizations reveal that the improved PEC efficiency is mainly attributed to the well-designed coordinatively unsaturated Co2+ sites, which not only serve as powerful photohole extraction engines along reversed interfacial Co-O-Bi bonds to promote charge transfer across the BiVO4/complex interface but also act as reaction active centers by accelerating surface water oxidation kinetics. This work provides new insights for designing highly effective OECs for PEC water oxidation.

Synergy Effect of the Enhanced Local Electric Field and Built-In Electric Field of CoS/Mo-Doped BiVO4 for Photoelectrochemical Water Oxidation.

Bismuth vanadate is a promising material for photoelectrochemical water oxidation. However, it suffers from a low quantum efficiency, poor stability, and slow water oxidation kinetics. Here, we developed a novel photoanode of CoS/Mo-BiVO4 with excellent photoelectrochemical water oxidation performance. It achieved a photocurrent density of 4.5 mA cm-2 at 1.23 V versus the reversible hydrogen electrode, ∼4 times that of BiVO4. The CoS/Mo-BiVO4 photoanode also exhibited good stability, and the photocurrent density generated by the CoS/Mo-BiVO4 photoanode did not significantly decrease after light irradiation for 2 h. Upon replacement of part of the V with Mo doping in BiVO4, the local electric field around the Mo-O bond was enhanced, thus promoting carrier separation in BiVO4. The CoS was deposited on the surface of Mo-BiVO4, forming a built-in electric field at the interface. Under the action of the bias electric field and the built-in electric field, the carriers of CoS/Mo-BiVO4 were efficiently separated in the direction of the inverse type II heterojunction. In addition, CoS improved the light absorption and charge injection efficiency of the CoS/Mo-BiVO4 photoanode.

Extremely low onset potential of modified Fe2O3 photoanode for water oxidation

The photoelectrochemical (PEC) performance of hematite (α-Fe2O3)-based photoanodes is still far from its theoretical value because they are constrained by serious charge recombination and sluggish water oxidation kinetics. Herein, we developed a heterostructural photoanode by coating boron doped graphite carbon nitride nanolayers onto an Fe2O3 nanoarray (BCN/Fe2O3), followed by modification with NiCo(OH)x cocatalyst. The constructed NiCo(OH)x/BCN/Fe2O3 demonstrates a significantly improved photocurrent density of 2.7 mA cm−2 at 1.23 VRHE (V versus reversible hydrogen electrode), which is 3.2 times higher than that of pristine Fe2O3. Additionally, it exhibits an extremely negative onset potential of 0.60 VRHE. Detailed studies reveal that the BCN/Fe2O3 heterojunction endows a driving force for charge separation and establishes a direct pathway for their transport, while NiCo(OH)x acts as a cocatalyst to accelerate the surface water oxidation reaction.

Synergistic effect between the iron (III) oxyhydroxide and Gd-Fe2O3 photoanode interface resulted in an ultra-low onset potential for photoelectrochemical water oxidation

The onset potential is an important descriptor of the photoelectrochemical water oxidation performance of photoanodes. Herein, we prepared Gd-doped hematite (Gd-Fe2O3)/iron (III) oxyhydroxide (FeOOH) core-shell photoanodes by in-situ isovalent doping and secondary hydrothermal treatment. This Gd-Fe2O3/FeOOH photoanode shows a record alkaline water oxidation onset potential (0.59 V vs. reversible hydrogen electrode) in hematite-based photoanodes and a 2.4-fold increase in photocurrent density over pristine hematite. Detailed studies demonstrate that the origin of the ultra-low onset potential is mainly attributed to the synergistic effect of isovalent Gd-doping and FeOOH cocatalyst. Specifically, Gd doping enhances donor density and reduces charge transport resistance, and FeOOH cocatalyst significantly improves water oxidation kinetics. In addition, the strong interfacial coupling of FeOOH and Gd-Fe2O3 promotes electron flow, which also improves the charge separation remarkably. This work gives hope for the achievement of stable and bias-free hematite-based photoanodes.

Enhancing the photoelectrochemical activity and stability of plate-like WO3 photoanode in neutral electrolyte solution using optimum loading of BiVO4 layer and NiFe–LDH electrodeposition

Tungsten trioxide (WO3) is an attractive candidate that can be used as a photoanode in the photoelectrochemical (PEC) water splitting device. However, WO3 photoanode is known for its high thermodynamic and chemical stability only in strong acidic (low pH) electrolyte solution and its relatively wide bandgap energy (2.8 eV) leads to insufficient absorption of visible light. The current study explored a WO3/BiVO4 heterojunction photoanode, consisting of plate-like WO3 covered with a uniform and highly porous BiVO4 thin layer, with electrodeposition of NiFe–LDH as a co-catalyst for oxygen evolution reaction. This top layer of BiVO4 nanostructure not only exhibited an enhancement in absorption of visible light but also protected the underneath plate-like WO3 from being attacked by the neutral environment of electrolyte solution (pH=∼7), resulting in significant improvement in its stability. The electrodeposition of NiFe–LDH using an acidic aqueous electrolyte solution (pH=3.7) was employed to overcome the sluggish kinetics of water oxidation on the surface of BiVO4. To overcome the weakness of the chemical dissolution of BiVO4 nanostructure in strong acidic solution, the electrodeposition time was carefully optimized for 50 s, leading to a uniform distribution of co-catalyst on the surface of WO3/BiVO4 heterostructure without the dissolving of BiVO4 in the acidic media. The WO3/BVO5/NiFe50 photoanode with the highest PEC performance (photocurrent density of around 1.78 mA/cm2 at 1.23 V vs. RHE) could maintain around 75% of its initial photocurrent after 24 h.

Accurate design of spatially separated double active site in Bi4NbO8Cl single crystal to promote Z - Scheme photocatalytic overall water splitting

The efficiency of photocatalytic overall water splitting was mainly limited by the slow reaction kinetics of water oxidation. How to design effective surface active site to overcome the slow water oxidation reaction was a major challenge. Here, we propose a strategy to accelerate surface water oxidation through the fabrication spatially separated double active sites. FeCoPi/Bi4NbO8Cl-OVs photocatalyst with spatially separated double active site was prepared by hydrogen reduction photoanode deposition method. Due to the high matching of the spatial loading positions of FeCoPi and OVs with the photogenerated charge distribution of Bi4NbO8Cl and corresponding reaction mechanisms of substrate, the FeCoPi and OVs on the (001) and (010) crystal planes of Bi4NbO8Cl photocatalyst provided surface active site for water oxidation reaction and electron shuttle reaction (Fe3+/Fe2+), respectively. Under visible light irradiation, the evolution O2 rate of FeCoPi/Bi4NbO8Cl OVs was 16.8 μmol h−1, as 32.9 times as Bi4NbO8Cl. Furthermore, a hydrogen evolution co-catalyst PtRu@Cr2O3 was prepared by sequential photodeposition method. Due to the introduction of Ru, the Schottky barrier between PbTiO3 and Pt was effectively reduced, which promoted the transfer of photogenerated electrons to PtRu@Cr2O3 thermodynamically, the evolution H2 rate on PtRu@Cr2O3/PbTiO3 increased to 664.8 times. On based of the synchronous enhancement of the water oxidation performance on FeCoPi/Bi4NbO8Cl-OVs and water reduction performance on PtRu@Cr2O3/PbTiO3, a novel Z - Scheme photocatalytic overall water splitting system (FeCoPi/Bi4NbO8Cl-OVs) mediated by Fe3+/Fe2+ had successfully constructed. Under visible light irradiation, the evolution rates of H2 and O2 were 2.5 and 1.3 μmol h−1, respectively. This work can provide some reference for the design of active site and the controllable synthesis of OVs spatial position. On the other hand, the hydrogen evolution co catalyst (PtRu@Cr2O3) and the co catalyst FeCoPi for oxygen evolution contributed to the construction of an overall water splitting system.

Bifunctional Co-TiO2 co-promoted bulk and interfacial charge transfer of BiVO4 photoanodes for solar water oxidation

The primary causes of photogenerated carrier recombination in BiVO4 photoanodes are the formation of bulk polarons and sluggish water oxidation kinetics. To address these issues effectively, we designed a bifunctional Co-TiO2 to modify the BiVO4 photoanodes. UV–vis DRS and Mott-Schottky results indicate that Co adjusts the band gap of TiO2, and there forms a type-II heterojunction between BiVO4 and Co-TiO2. The experimental tests and theoretical calculations for OER as well as EIS results demonstrate that Co sites in Co-TiO2 provide more reaction sites for the interfacial oxidation reaction, reducing the overpotential. Under the dual action of Co-TiO2, the co-promotion for the migration ability of photogenerated carriers in the bulk and on the surface of BiVO4 photoanode has been realized. This conclusion is supported by analysis of photogenerated charge transfer behavior through transient photocurrent and IMPS. As a result, the photogenerated current density of BiVO4/Co7 %-TiO2 photoanode reaches 4.38 mA cm−2 at 1.23 V vs. RHE under AM 1.5 G illumination, which is four times that of pure BiVO4 photoanodes.

Determining the Transformation Kinetics of Water Oxidation Intermediates on Hematite Photoanode.

The oxygen evolution reaction (OER) from water is a sequential oxidation reaction process, involved in transformation of multiple reaction intermediates. For photo(electro)catalytic OER, revealing the intermediates transformation kinetics is quite challenging due to its coupling with photogenerated charge dynamics. Herein, we specifically study the transformation kinetics of the OER intermediates in rationally thin hematite photoanodes through increasing the ratio between surface intermediates and photogenerated charges in bulk. We directly identify the formation and consumption kinetics of one-hole OER intermediate (FeIV═O) in photoelectrochemical water oxidation using operando transient absorption (TA) spectroscopy. The microsecond formation kinetics of the FeIV═O species are sensitively changed by the excitation mode of Fe2O3. The subsecond consumption kinetics are closely dependent on surface FeIV═O species density, demonstrating that the cooperation of FeIV═O intermediates is the key to accelerating water oxidation kinetics on the Fe2O3 surface. This work provides insight into understanding and controlling water oxidation reaction kinetics on Fe2O3 surface.

(Invited) Understanding the Effects of Charge Distribution on the Oxidation of Water

Water oxidation is an important first step of photosynthesis. Presently, it remains a challenge to carry out this reaction efficiently using low-cost materials. Among the questions that remain to be answered are the influences by charge distribution at or on the catalyst surfaces where water oxidation takes place. Recent literature has shown that the reaction can be sensitive to the charge density or the charge potential or both. Generally, high charge density or high charge potential favors faster kinetic constants. However, the existing studies face challenges as most of them were carried out on different materials that feature different chemical catalytic properties, as well. As such, it is not yet possible to definitely conclude the observed differences in water oxidation kinetics is necessarily a function of charge properties but not the inherent chemical catalytic differences. The study we plan to present addresses this issue. We used a catalyst system that features a well-defined catalytic center but employed supports that feature varying charge redistribution properties. This system allowed us to systematically compare how charge redistribution affects the water oxidation reactions. It was observed that when charge redistribution indeed plays an important role in defining the reaction kinetics, but it is so only when the subsequent chemical steps are fast. For the first time, we found a different dependence of the reaction kinetics on temperatures. Under otherwise identical conditions, comparable reaction kinetics were measured on ITO support and CeO2 support at room temperature. When the temperature increased to 50ºC, the reaction rate on ITO support increased to twice that on CeO2 support. The results shed new light on the role played by charge redistribution in governing reactions such as water oxidation.

Observation of Support-Dependent Water Oxidation Kinetics on Molecularly-Derived Heterogeneous Ir-Oxide Catalysts

Heterogeneous water oxidation catalysis is central to the development of renewable energy technologies. Understanding the material properties that determine water oxidation activity is critically important for the design of efficient and durable water oxidation catalysts. The electronic structure and surface chemistry of the catalyst influence the accumulation of oxidative charge (holes) on catalytically active sites. Hole distribution dynamics and molecular structure of the active sites are generally accepted to jointly determine activity. However, these properties are typically inherent to materials; it has been difficult to independently tune them on most heterogeneous catalysts, hindering the development of an understanding of their relative influence. Herein, heterogenized dinuclear Ir catalysts (Ir-DHC) supported on different oxides were employed to overcome this challenge. It was found that at low temperatures (288-298 K), the photocatalytic activities of Ir-DHC on indium tin oxide (ITO) and CeO2 supports are comparable within the studied range of fluences (62-151 mW/cm2). By contrast, at higher temperatures (310-323 K), Ir-DHC on ITO exhibits a ∼100% higher water oxidation activity than on CeO2. The divergent activities under these conditions were attributed to the distinct abilities of the supporting substrates to redistribute surface holes. Specifically, ITO is relatively efficient in distributing photogenerated holes between Ir-DHC active sites, whereas CeO2 exhibits sluggish hole redistribution because of its reducibility, thereby limiting hole accumulation at Ir-DHC active sites. The temperature dependence was explained by a temperature induced switch in the rate-determining step of the reaction. These findings highlight the critical role of the supporting substrate in determining the turnover at active sites of heterogeneous catalysts.

TiO2 nanorod/nanotube interface reconstruction and synergistic role of oxygen vacancies and gold in H–Au–TiO2 NR/NT for photoelectrochemical bacterial inactivation and water splitting

Photoelectrochemical (PEC) water splitting by semiconductor photoanodes is limited by sluggish water oxidation kinetics coupled with serious charge recombinations. In this paper, an effective strategy of TiO2 nanorod/nanotube nanostructured interface reconstruction, oxygen vacancies and surface modification were employed for stability and efficient charge transport in the photoanodes. Successive anodization and hydrothermal routes were adopted for the TiO2 NR/NT photoanodes interface reconstruction, followed by Au nanoparticles/clusters (Au NP) loading and hydrogen treatment. This resulted in H–Au–TiO2 NR/NT photoanodes. A three-dimensional structure of TiO2 NR on TiO2 NT/Ti foil nanotubes achieved the highest photocurrent density (1.42 mA cm−2 at 0.3 V vs. Ag/AgCl). The optimal oxygen vacancies and Au NP loading on TiO2 NR/NT exhibited 1.62 mA cm−2 photocurrent density at 0.3 V vs. Ag/AgCl in H–Au–TiO2 NR/NT photoelectrode, which is eight times higher than the TiO2 NT/Ti foil. TRPL analyses confirm the hydrogen treatments to TiO2 exhibited the emission lifetime (46 ns) in the H–Au–TiO2 NR/NT photoanodes due to newly formed lower Ti3+-related trapped electron states and Au NP. The optimum H–Au (4)–TiO2 NR/NT photoanodes achieved 95% photoelectrochemical (PEC) bacterial inactivation and effective PEC water splitting with (278 and 135.4) μmol of hydrogen and oxygen generation, respectively. In this study, oxygen vacancies combined with gold particles and interface reconstruction provide an innovative way to design effective photoelectrodes.

Citrate modulation of CoAl(OH)x Catalyst/Sb–TiO2 nanorods interface boosting photocarrier separation and injection for enhanced water oxidation

The design of an oxygen evolution catalyst (OEC) coupled photoanode ensuring effective charge separation, transfer, and injection is always desirable for enhanced water oxidation kinetics. Here, we have designed Sb-doped TiO2 nanorods (NRs) photoanode coupled with the ultrathin amorphous CoAl(OH)x OEC via citrate anion bridging. The CoAl(OH)x performs as a hole scavenger OEC, a hole storage layer, surface defect passivation layer, and also generates a band banding leading to the built-in potential at the semiconductor/catalyst interface favoring rapid hole separation. The citrate linking improves the CoAl(OH)x/Sb–TiO2 interfacial bonding and reduces the interfacial impedance to boost the photocarrier separation. Citrate bridging also serves as an efficient hole extraction layer and transportation pathway and promotes oxygen vacancy formation, which favors adsorbing OH− during the OER. As a result, the CoAl(OH)x/cit/Sb–TiO2 NRs photoanode exhibits a superior photocurrent density of 1.73 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (VRHE), close to the theoretical maxima of titanium dioxide, with a very low onset potential of 0.12 VRHE and an extremely high hole injection efficiency of 93.1%. This work demonstrates an effective design strategy to boost the performance of OER catalyst coupled photo harvesting semiconductor photoanodes to achieve efficient solar water splitting.

Bifunctional photothermal effect to promote band bending and water oxidation kinetics for improving photoelectrochemical water splitting

The photothermal effect is proved to favor the photoelectrochemical (PEC) water oxidation, but the impact of the photothermal effect on the band bending in the heterojunction has seldom been revealed. In this work, we constructed a Z schematic heterojunction by heteroatoms doping, the carbon quantum dots (CQDs) was anchored to trigger the local heat under the NIR irradiation. With the photothermal effect, the photocurrent density of (Ti, Zn)–Fe2O3@Ti–Fe2O3 reached 1.02 mA/cm2 (1.23 VRHE), 2.30 mA/cm2 (1.60 VRHE), which yielded an increased by 1.3 folds, 1.7 folds, respectively. Detailed studies showed that the photothermal effect would enlarge the contact potential difference in the heterojunction and band bending at the semiconductor-electrolyte interface (SEI). Furthermore, the oxygen evolution reaction (OER) kinetics was also accelerated, which was evidenced by the Tafel slope decreasing from 88 mV/decade to 78 mV/decade. Despite the photovoltage being reduced, the advantages of the photothermal effect still out weighted the disadvantages.

Facilitating photogenerated carrier transfer and water oxidation kinetics of BiVO4 photoanode via novel Zn@Co3C functional layer

Currently, the sluggish charge transfer kinetics and water oxidation kinetics are still the bottlenecks faced by BiVO4 photoanodes at present. Herein, an excellent Zn@Co3C functional layer is reported for the first time to tackle these problems of BiVO4 photoanode. Zn@Co3C was prepared using a facile electrochemical method with 1,2-dimethylimidazole as a carbon source. In the BiVO4/Zn@Co3C photoanode, Co3C acts as a novel oxygen evolution co-catalyst to significantly enhance water oxidation kinetics. An electron depletion layer formed around Zn species provides a strong driving force for the migration of photogenerated holes from BiVO4 to Co3C catalytic sites. Furthermore, the alternating distribution of Co3C and Zn species on the surface of BiVO4 photoanodes increases the utilization efficiency of Co3C co-catalyst. The BiVO4/Zn@Co3C system constructed in this work not only demonstrates good photoelectrochemical performance in electrolytes (4.6 mA cm−2 at 1.23 V vs. RHE without any hole scavengers), but also enables water splitting in natural seawater. This work demonstrates a novel functional layer that simultaneously facilitates photogenerated carrier transfer and water oxidation kinetics, which holds great promise for constructing high-performance water oxidation systems in various photoanodes.

Suppression of Undesired Losses in Organometal Halide Perovskite‐Based Photoanodes for Efficient Photoelectrochemical Water Splitting

Organometal halide perovskites (OHPs) have become potential candidates for high‐efficiency photoelectrodes for use in photoelectrochemical (PEC) water splitting. However, undesired losses, such as the non‐radiative recombination of photogenerated carriers and sluggish reaction kinetics of PEC water splitting, are the main limitations to achieving maximum efficiency for OHP‐based photoelectrodes. Herein, high‐efficiency OHP‐based photoanodes with a rational design that suppresses the undesired losses is reported. As a rational design for OHP‐based photoanodes, the defect‐passivated electron transport layers effectively suppress the undesired recombination of photogenerated carriers from the OHP layers. In addition, Fe‐doped Ni3S2 with a high catalytic activity promotes the reaction kinetics of PEC water oxidation, thereby suppressing the undesired losses at the interface between the OHP photoanodes and electrolytes. The fabricated Fe‐doped Ni3S2/Ni foil/OHP photoanodes exhibit a remarkable applied bias photon‐to‐current efficiency of 12.79%, which is the highest of the previously reported OHP‐based photoanodes by suppressing undesired losses. The strategies for achieving high‐efficiency OHP‐based photoanodes provide insights into the rational design of photoelectrodes based on OHPs.

Scalable ambient conditions-based fabrication of flower-like bismuth vanadate (BiVO4) film incorporating defects aimed at visible-light-induced water-splitting application

The scalable application of bismuth vanadate (BiVO4) in photoelectrochemical water splitting is restricted by its low charge separation efficiency and slow water oxidation kinetics. Here, modified BiVO4 photoanodes were fabricated at ambient conditions with polyethylene glycol (PEG) and potassium hydroxide (KOH) for improving the electron-hole generation rate and lowering the charge carrier recombination rate. Modification by PEG produced 3D flower-like BiVO4 microspheres, along with Bi5+, Bi(3−x)+, and V4+ species onto the PEG-BiVO4 surface, which were accompanied by oxygen vacancies (OVs) working in tandem with these species and acting as surface-active intermediates, thereby facilitating hole transfer to the electrolyte. Under visible light irradiation (100 mW/cm2), 3D flower-like PEG-BiVO4 microspheres produce the maximum photocurrent density of 5.75 mA/cm2 in water splitting at 1.23 V against a reverse hydrogen electrode (RHE). The superior photoelectrochemical performance of PEG-BiVO4 over its counterparts is attributed to the incorporation of 3D flower-like microspheres and band structure modulation by the O vacancies, Bi(3−x)+, Bi5+, and V4+ species. The synthesized PEG-BiVO4 is expected to attract attention as a scalable photocatalyst for oxidation of water because it is easy to synthesize at room temperature and it exhibits superb photocatalytic performance.

Photoelectrochemical water oxidation through a hybrid architecture nanoparticles/nanotubes

Sunlight is the cleanest and largest source of energy, even if the sunlight is somewhat unpredictable. Indeed, photoelectrochemical (PEC) water splitting affords a clean, carbon–neutral process, even if complex, to achieve the transform of photons in chemical energy (H2). The true limitation of the process is related to the conversion in energy storage. In this work, we exploit Co-P nanoparticles and TiO2 nanotubes, and additional modifications. Using organic species, including hexane, oleylamine, and hydrazine, control of the capping ligand of the TiO2 nanotubes is achieved, allowing maximum order. Optimizing the deposition of Co-P nanoparticles, and by increasing the rate of water oxidation kinetics, the photocurrent saturated current density is improved by 1.15-fold. Additionally, a further modification at the surface of the TiO2 NTs by Ar-ion sputtering is demonstrated to improve the overall photo-saturated photocurrent density up to 1.7-fold of the TiO2 NTs deposited with Co-P nanoparticles. Finally, a further modification at the surface of the TiO2 NTs by Ar-ion sputtering is demonstrated to improve the overall photo-saturated photocurrent density.

Surface Self-Transforming FeTi-LDH Overlayer in Fe2 O3 /Fe2 TiO5 Photoanode for Improved Water Oxidation.

Integrating hematite nanostructures with efficient layer double hydroxides (LDHs) is highly desirable to improve the photoelectrochemical (PEC) water oxidation performance. Here, an innovative and facile strategy is developed to fabricate the FeTi-LDH overlayer decorated Fe2 O3 /Fe2 TiO5 photoanode via a surface self-transformation induced by the co-treatment of hydrazine and NaOH at room temperature. Electrochemical measurements find that this favorable structure can not only facilitate the charge transfer/separation at the electrode/electrolyte interface but also accelerate the surface water oxidation kinetics. Consequently, the as-obtained Fe2 O3 /Fe2 TiO5 /LDH photoanode exhibits a remarkably increased photocurrent density of 3.54mAcm-2 at 1.23V versus reversible hydrogen electrode (RHE) accompanied by an obvious cathodic shift (≈140mV) in the onset potential. This work opens up a new and effective pathway for the design of high-performance hematite photoanodes toward efficient PEC water oxidation.

Heterostructured CoFe1.5Cr0.5S3O/COFs/BiVO4 photoanode boosts charge extraction for efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting can convert the inexhaustible solar energy into green and storable H2 to tackle fossil crisis and meet carbon neutrality. BiVO4 is regarded as a promising photoanode owing to its superior visible light absorption, moderate redox potentials and well chemical stability, but suffering from the rapid recombination of charge carriers and sluggish interfacial water oxidation kinetics. Herein, a heterostructured CoFe1.5Cr0.5S3O/COFs/BiVO4 photoanode was fabricated to accelerate charge carriers′ separation and boost water oxidation. The spinel-type CoFe1.5Cr0.5S3O serving as the co-catalyst enabled to largely lower the overpotential of water oxidation, while COFs acting as an interlayer passivated the interfacial defect between CoFe1.5Cr0.5S3O and BiVO4. Benefiting from the collaboration of CoFe1.5Cr0.5S3O co-catalyst and COFs interlayer, heterostructured CoFe1.5Cr0.5S3O/COFs/BiVO4 photoanode featuring with a prominent charge extraction efficiency reached an impressive water oxidation photocurrent of 5.1 mA cm−2 at 1.23 V vs. RHE under AM 1.5 G irradiation, higher than that of pristine BiVO4, binary COFs/BiVO4 and CFCOS/BiVO4 photoanodes. This work demonstrated that heterostructured BiVO4-based photoanode with co-catalyst and interlayer enables to simultaneously enhance charge carrier utilization efficiency and optimize surface catalysis kinetics for efficient solar-to-fuel conversion.

PH-Responsive Flexible Copper Electrode with Switchable Wettability for Electrocatalytic Hydrogen/Oxygen Evolution Reactions and Urea Oxidation Reaction.

The development of a pH-responsive electrode with switchable wettability is of great importance in water electrolysis. Here, we designed a pH-responsive copper mesh/copolymer electrode to eliminate the adhesion of hydrogen/oxygen bubbles under high-speed water electrolysis by adjusting the wettability of the electrode surface. Furthermore, the kinetics of water oxidation and urea oxidation reactions on the as-prepared copper mesh/copolymer electrode were explored. Most noteworthy, the flexible water electrolysis performance of the as-prepared pH-responsive electrode was investigated for the first time. The results indicate that the copper mesh/copolymer electrode accelerates the hydrogen evolution reaction, oxygen evolution reaction, and urea oxidation reaction under better surface wettability, while it inhibits these reactions under poor surface wettability. The results provide insight into the development of unusual water electrolyzers with different pH electrolytes and the design of water electrolysis electrodes.