A tungsten phosphide cocatalyst enhanced bismuth tungstate photoanode with the robust built-in electric field towards highly efficient photoelectrochemical water splitting

The use of low-cost and effective cocatalyst is a potential strategy to optimize the effectiveness of photoelectrochemical (PEC) water splitting. In this study, tungsten phosphide (WP) is introduced as a remarkably active cocatalyst to enhance the PEC efficiency of a Bi2WO6 photoanode. The onset potential of Bi2WO6/WP demonstrates a negative shift, while the photocurrent density demonstrates a significant 5.5-fold increase compared to that of unmodified Bi2WO6 at 1.23 VRHE (reversible hydrogen electrode). The loading of WP cocatalyst facilitates the rapid transfer of holes, increasing the range of visible light absorption, the water adsorption ability as well as promoting the separation of photogenerated electrons and holes via the built-in electric field between Bi2WO6 and WP. This study proposes a strategy to hinder the recombination of electron-hole pairs by using WP cocatalyst as a hole capture agent, improve the photoelectric conversion efficiency, and enhance the overall photoelectrochemical properties of Bi2WO6 photoanode.

Structurally disordered MoSe2 with rich 1T phase as a universal platform for enhanced photocatalytic hydrogen production

The improvement of surface reactivity in noble-metal-free cocatalysts is crucial for the development of efficient and cost-effective photocatalytic systems. However, the influence of crystallinity on catalytic efficacy has received limited attention. Herein, we report the utilization of structurally disordered MoSe2 with abundant 1T phase as a versatile cocatalyst for photocatalytic hydrogen evolution. Using MoSe2/carbon nitride (CN) hybrids as a case study, it is demonstrated that amorphous MoSe2 significantly enhances the hydrogen evolution rate of CN, achieving up to 11.37 μmol h-1, surpassing both low crystallinity (8.24 μmol h-1) and high crystallinity MoSe2 (3.86 μmol h-1). Experimental analysis indicates that the disordered structure of amorphous MoSe2, characterized by coordination-unsaturated surface sites and a rich 1T phase with abundant active sites at the basal plane, predominantly facilitates the conversion of surface-bound protons to hydrogen. Conversely, the heightened charge transfer capacity of the highly crystalline counterpart plays a minor role in enhancing practical catalytic performance. This approach is applicable for enhancing the photocatalytic hydrogen evolution performance of various semiconducting photocatalysts, including CdS, TiO2, and ZnIn2S4, thereby offering novel insights into the advancement of high-performance non-precious catalysts through phase engineering.

NiCS3: A cocatalyst surpassing Pt for photocatalytic hydrogen production

Cocatalysts play a key role in improving photocatalytic performance by enhancing conductivity and providing an enormous number of active sites simultaneously. However, cocatalysts are usually made of noble metals such as Pt, which are expensive and rare. Therefore, cocatalysts derived from cheap and abundant elements are highly desirable. Here, for the first time, we demonstrate that NiCS3, which is made from nickel that is abundant and costs less than 0.04 % of Pt, is an effective substitute for Pt cocatalysts for the photocatalytic activity of CdS nanorods in hydrogen evolution reaction (HER). Under visible light, the NiCS3/CdS composite with NiCS3 as the cocatalyst achieved an astonishing H2 production of 61.9 mmol·g-1·h-1 while maintaining high stability, which is 14 times higher than that observed when using CdS alone and nearly 2 times higher than that of Pt/CdS. We also established that the metallicity of NiCS3 results in good carrier conductivity, which promotes the electron transfer and the separation of photo-induced carriers. Due to the appropriate adsorption energy ΔGH*, NiCS3 more readily adsorbs hydrogen protons and desorbs molecular hydrogen during the photocatalytic process compared with Pt. Additionally, NiCS3 can effectively inhibit the photo-corrosion effect of CdS itself, ensuring a good stability of HER. These results suggest that NiCS3 is a promising substitute for Pt cocatalysts.

Stabilizing electron-rich Ni single-atoms on black phosphorus nanosheets boosts photocatalytic carbon dioxide reduction

The development of unique single-atom catalysts with electron-rich feature is essential to promoting the photocatalytic CO2 reduction, yet remains a big challenge. Here, a conceptionally new single-atom catalyst constructed from atomically dispersed Ni-P3 species on black phosphorus (BP) nanosheets (BP-Ni) is synthesized for realizing highly efficient visible-light-driven CO2 reduction when trapping photogenerated electrons from homogeneous light absorbers in the presence of triethanolamine as the sacrificial agent. Both the experimental and theoretical calculation data reveal that the Ni-P3 species on BP nanosheets own the electron-rich feature that can improve the photogenerated charge separation efficiency and lower the activation barrier of CO2 conversion. This unique feature makes BP-Ni exhibit the much higher activity as cocatalyst in the photocatalytic CO2 reduction than BP nanosheets. The BP-Ni can also be applied as a cocatalyst for enhanced photocatalytic CO2 reduction after combining with CdSe/S colloidal crystal photocatalyst. The present study offers valuable inspirations for the design and construction of effective catalytic sites toward photocatalytic CO2 reduction reactions.

Composites of (NH2)-MIL-53(Al) and CBB as bifunctional electrocatalysts for overall electrochemical water splitting in all pH solutions

Electrochemical water splitting is one of the most active areas of energy research, yet the benchmark electrocatalysts used for this area are based on expensive noble metals and transition metals, thus mainly reactions in alkaline solution. MOFs and halide perovskite are novel electrochemical catalysts but unstable in water basically. Here we report a study on composites of (NH2)-MIL-53(Al) MOFs and CBB halide perovskite (Cs3Bi2Br9), which exhibit obvious activity for overall electrochemical water splitting for long-term stability with little deactivation after 10 h in all pH solutions.

Construction of 2D/1D Cu7S4 nanosheets/Mn0.3Cd0.7S nanorods heterojunction for highly efficient photocatalytic hydrogen evolution

Developing cost-effective cocatalyst-modified photocatalytic systems with boosted carrier separation and rapid surface catalytic reaction is an ideal strategy for effectively converting solar energy into desired fuels. Herein, a series of Cu7S4/Mn0.3Cd0.7S hierarchical heterostructures are designed and fabricated to achieve efficient and robust photocatalytic H2 evolution by coupling one-dimensional (1D) Mn0.3Cd0.7S nanorods with two-dimensional (2D) Cu7S4 nanosheets through a facile sonochemical strategy. Benefiting from dimensionality and cocatalyst effects, the constructed 2D/1D Cu7S4/Mn0.3Cd0.7S heterojunction photocatalyst containing 1.5 wt% Cu7S4 displays excellent photostability and superior photocatalytic H2 evolution rate up to 914.3 μmol h-1, which is 4.43 and 2.22-folds increment relative to bare Mn0.3Cd0.7S and the 3 wt% Pt/Mn0.3Cd0.7S, respectively. The various characterization results reveal that the utilization of semimetallic Cu7S4 nanosheets as the cocatalyst to form a Schottky heterojunction can promote the light-harvesting capability, suppress charge carrier recombination, and provide sufficient reaction sites for hydrogen generation, thereby resulting in the dramatically improved photocatalytic performance. This work clarifies the role of Cu7S4 nanosheets as the robust and cost-effective cocatalyst in the photocatalytic reaction and opens a new horizon for designing other Cu7S4-based cocatalyst/semiconductor Schottky heterostructures for efficient solar-to-fuel conversion.

An Oxysulfide Photocatalyst Evolving Hydrogen with an Apparent Quantum Efficiency of 30 % under Visible Light

Photocatalytic water splitting is a simple means of converting solar energy into storable hydrogen energy. Narrow-band gap oxysulfide photocatalysts have attracted much attention in this regard owing to the significant visible-light absorption and relatively high stability of these compounds. However, existing materials suffer from low efficiencies due to difficulties in synthesizing these oxysulfides with suitable degrees of crystallinity and particle sizes, and in constructing effective reaction sites. The present work demonstrates the production of a Gd2 Ti2 O5 S2 (λ<650 nm) photocatalyst capable of efficiently driving photocatalytic reactions. Single-crystalline, plate-like Gd2 Ti2 O5 S2 particles with atomically ordered surfaces were synthesized by flux and chemical etching methods. Ultrafine Pt-IrO2 cocatalyst particles that promoted hydrogen (H2 ) and oxygen (O2 ) evolution reactions were subsequently loaded on the Gd2 Ti2 O5 S2 while ensuring an intimate contact by employing a microwave-heating technique. The optimized Gd2 Ti2 O5 S2 was found to evolve H2 from an aqueous methanol solution with a remarkable apparent quantum efficiency of 30 % at 420 nm. This material was also stable during O2 evolution in the presence of a sacrificial reagent. The results presented herein demonstrates a highly efficient narrow-band gap oxysulfide photocatalyst with potential applications in practical solar hydrogen production.

A Medium-entropy oxide as a promising cocatalyst to promote photocatalytic hydrogen evolution

As emerging materials, medium-entropy oxides have attracted wide attention for the huge potential in energy storage, catalytic, magnetic and thermal applications. The electronic effect or the strong synergic effect caused by the construction of medium-entropy system leads to the unique properties of catalysis. In this contribution, we reported a medium-entropy CoNiCu oxide as an efficient cocatalyst for enhanced photocatalytic hydrogen evolution reaction. The target product was synthesized by a process of laser ablation in liquids and graphene oxide was applied as a conductive substrate of it, then it was loaded on the photocatalyst g-C₃N₄. The results showed that the modified photocatalysts exhibited the reduced [Formula: see text] and enhanced abilities of photoinduced charges separation and transfer. Furthermore, a maximum hydrogen production rate was measured to be 1177.52 μmol ·g^-1·h^-1 under the visible light irradiation, which was about 291 times higher than that of pure g-C₃N₄. These findings suggest that the medium-entropy CoNiCu oxide serves as an eminent cocatalyst, which offers a possible pathway towards the broadening of the applications of medium-entropy oxides and provides the alternatives to conventional cocatalysts.

Enhanced piezocatalytic hydrogen evolution performance of bismuth vanadate by the synergistic effect of facet engineering and cocatalyst engineering

Developing piezocatalysts with excellent piezocatalytic hydrogen evolution reaction (HER) performance is highly desired but also challenging. Here, facet engineering and cocatalyst engineering are employed to synergistically improve the piezocatalytic HER efficiency of BiVO₄ (BVO). Monoclinic BVO catalysts with distinct exposed facets are synthesized by adjusting pH of hydrothermal reaction. The BVO with highly exposed {110} facet exhibits a superior piezocatalytic HER performance (617.9 μmol g^-1h^-1) compared with that with {010} facet, owing to the strong piezoelectric property, high charge transfer efficiency, and excellent hydrogen adsorption/desorption capacity. The HER efficiency is enhanced by 44.7% by selectively depositing cocatalyst of Ag nanoparticles specifically on the reductive {010} facet of BVO, where the Ag-BVO interface provides the directional electron transport for high-efficiency charge separation. Under the collaboration between cocatalyst of CoO_x on {110} facet and the hole sacrificial agent of methanol, the piezocatalytic HER efficiency is evidently enhanced by 2 times because CoO_x and methanol can impede the water oxidation and improve the charge separation. This easy and simple strategy provides an alternative perspective on designing high-performance piezocatalysts.

Dual modification of BiVO4 photoanode for synergistically boosting photoelectrochemical water splitting

Bismuth vanadate (BiVO₄) is a promising nanomaterial for photoelectrochemical (PEC) water oxidation. However, the serious charge recombination and sluggish water oxidation kinetics limit its performance. Herein, an integrated photoanode was successfully constructed by modifying BiVO₄ (BV) with In₂O₃ (In) layer and further decorating amorphous FeNi hydroxides (FeNi). The BV/In/FeNi photoanode exhibited a remarkable photocurrent density of 4.0 mA cm^-2 at 1.23 V_RHE, which is approximately 3.6 times larger than that of pure BV. And the water oxidation reaction kinetics has an over 200% increased. This improvement was mainly because the formation of BV/In heterojunction inhibited charge recombination, and the decoration of cocatalyst FeNi facilitated the water oxidation reaction kinetics and accelerated hole transfer to electrolyte. Our work provides another possible route to develop high-efficiency photoanodes for practical applications in solar conversion.

Surface anchoring of nickel sulfide clusters as active sites and cocatalysts for photocatalytic antibiotic degradation and bacterial inactivation

Achieving photocatalytic antibiotic degradation and bacterial inactivation with high efficiency remains a challenging mission to originate a clean environment. In this work, ultra-small NiS clusters were in-situ grew on photoactive ZnIn₂S₄ nanoflower supports to form a NiS/ZnIn₂S₄ heterojunction, in which a strong and surface-limited binding was formed between the NiS clusters and ZnIn₂S₄ supports. The in-situ formed NiS clusters not only appeased interfacial charge transfer resistance of the heterojunction but also eventuated a strong built-in electric field, resulting a fast electron migration from ZnIn₂S₄ to NiS clusters functioned as cocatalyst and active sites to boost the separation efficiency of photogenerated carriers. As a result, the optimal 2NiS/ZnIn₂S₄ heterojunction expressed a higher photocatalytic Escherichia inactivation activity (99.23 % for 3 h) and a raised antibiotic degradation performance, including tetracycline (60 % for 20 min), ofloxacin (62 % for 20 min), oxytetracycline (63 % for 20 min) compared to that of pure ZnIn₂S₄ (39.14 % for Escherichia inactivation and 44 % for tetracycline degradation). This work furnishes a great promise to develop inorganic clusters coupled photocatalysts for light-driven environmental application.

Reversing Free-Electron Transfer of MoS2+x Cocatalyst for Optimizing Antibonding-Orbital Occupancy Enables High Photocatalytic H2 Evolution

The interaction between cocatalyst-photocatalyst usually induces spontaneous free-electron transfer between them, but the effect and regulation of the transfer direction on the hydrogen-adsorption energy of active sites have not received attention. Herein, to steer the free-electron transfer in a favorable direction for weakening S-Hads bonds of sulfur-rich MoS2+x , an electron-reversal strategy is proposed for the first time. The core-shell Au@MoS2+x cocatalyst was constructed on TiO2 to optimize the antibonding-orbital occupancy. Research results reveal that the embedded Au can reverse the electron transfer to MoS2+x to generate electron-rich S(2+δ)- active sites, thus increasing the antibonding-orbital occupancy of S-Hads in the Au@MoS2+x cocatalyst. Consequently, the increase in the antibonding-orbital occupancy effectively destabilizes the H 1s-p antibonding and weakens the S-Hads bond, realizing the expedited desorption of Hads to rapidly generate a lot of visible H2 bubbles. This work delves deep into the latent effect of the photocatalyst carrier on cocatalytic activity.

2D Transition Metal Dichalcogenides for Photocatalysis

Two-dimensional (2D) transition metal dichalcogenides (TMDs), a rising star in the post-graphene era, are fundamentally and technologically intriguing for photocatalysis. Their extraordinary electronic, optical, and chemical properties endow them as promising materials for effectively harvesting light and catalyzing the redox reaction in photocatalysis. Here, we present a tutorial-style review of the field of 2D TMDs for photocatalysis to educate researchers (especially the new-comers), which begins with a brief introduction of the fundamentals of 2D TMDs and photocatalysis along with the synthesis of this type of material, then look deeply into the merits of 2D TMDs as co-catalysts and active photocatalysts, followed by an overview of the challenges and corresponding strategies of 2D TMDs for photocatalysis, and finally look ahead this topic.

Ag-enhanced CeF3-O: highly enhanced photocatalytic performance under NIR light irradiation

CeF₃-O with intermediate band showed improved synergic photodegradation activity toward HCl-TC and RhB under NIR light irradiation when enhanced by Ag as a cocatalyst. Ag⁺ ions take electrons from the second transition in CeF₃-O's intermediate band, which are then reduced to Ag as cocatalyst. The photodegradation efficiencies of HCl-TC by various Ag/CeF₃-O nanoparticles in 180-min increase from 26.5 to 73.1%. The optimal Ag/CeF₃-O-100 is about 2.76 times that of pure CeF₃-O. Ag/CeF₃-O-100 has an apparent rate constant of 4.5 × 10^-3 min^-1, which is 3.0 times that of pure CeF₃-O. Similarly, Ag/CeF₃-O-10 achieves a superior photodegradation efficiency of RhB at 96.7% under NIR light within 120 min. Its apparent rate constant of 27.7 × 10^-3 min^-1 is 12.0 times that of pure CeF₃-O (2.3 × 10^-3 min^-1). Further, the turnover frequencies of Ag/CeF₃-O nanoparticles are greatly higher than that of the corresponding pure CeF₃-O nanoparticles. Ag-enhanced CeF₃-O has a unique metal-semiconductor interface where Ag acts as a bridge for facilitating charge transfer and the separation efficiency of photogenerated carries. The synergic effect between CeF₃-O and Ag provides a practical technique for enhancing the wastewater treatment with NIR light irradiation.

Synergy of heterojunction and interfacial strain for boosting photocatalytic H2 evolution of black phosphorus nanosheets

As an emerging post-graphene two-dimensional material, black phosphorus (BP) has attracted enormous interest as a promising cocatalyst for photocatalytic hydrogen (H₂) evolution, however, the activity of either pristine bulk or BP nanosheets is far from satisfactory. Herein, we present an effective strategy to greatly boost the H₂ evolution performance of BP via applying the synergistic effect of heterojunction and interfacial lattice strain. A multilayered heterostructure coupling BP nanosheets and nickel oxide (NiO) nanosheets with abundant interface P-Ni and PO bonds is synthesized and utilized as a proof-of-concept material for our design. Both the experimental and theoretical results have revealed that the strain is formed in BP-NiO multilayered heterostructure. The generated lattice strain induces the charge redistribution at the interface between BP and NiO, which leads to the improved electron transfer efficiency and favorable H* adsorption kinetics for photocatalytic H₂ evolution reaction. As a result, the BP-NiO heterostructure with strain effect exhibits much enhanced photocatalytic H₂ evolution activity in the presence of Eosin Y (EY) as photosensitizer, exceeding that of zero-strained BP/NiO heterostructure and many other reported noble-metal-free cocatalyst.

Carbon hollow matrix anchored by isolated transition metal atoms serving as a single atom cocatalyst to facilitate the water oxidation kinetics of bismuth vanadate

Here, nitrogen doped carbon hollow matrix anchored by isolated transition metal atoms (M@NC, M = Fe, Co or Ni) are firstly utilized as new single atom cocatalysts (SACCs) to enhance the PEC performance of Mo, W ions co-doped BiVO₄ (Mo, W: BVO) through a simple spin-coating method. It is found that Mo, W: BVO modified with Fe@NC exhibits higher photocurrent density than the one decorated with Co@NC or Ni@NC due to the relatively low redox potential of Fe³⁺/Fe²⁺ (0.77 V vs SHE). During the photoelectrochemical (PEC) process, the Fe²⁺ ions are easier to accept the photogenerated holes of BVO and be oxidized to Fe³⁺ ions. Then, Fe³⁺ ions are reduced to Fe²⁺ again by accepting the electrons of water, and evolve oxygen simultaneously. Hence, Fe@NC could facilitate the water oxidation kinetics through the redox cycle of Fe ions and promote the charge separation efficiency by capturing the photogenerated holes. Theoretical calculations demonstrate that the deposition of Fe atoms make NC negatively charged, which is conducive to receiving the photogenerated holes. As a result, Mo, W: BVO/Fe@NC exhibits higher photocurrent density (3.2 mA/cm² vs RHE) than other BVO-based samples. This work opens up a new application field of SACCs serving as OER cocatalysts, and may provide a universal strategy to construct the efficient PEC photoelectrodes.

Dual-doping in the bulk and the surface to ameliorate the hematite anode for photoelectrochemical water oxidation

Aiming at the drawbacks of hematite like poor conductivity and tardy oxidation kinetics, herein, we utilized dual dopants in the bulk and surface to ameliorate the situation. Specifically, doping optimal amount of Zr⁴⁺ in the hematite (Zr:Fe₂O₃) enhances the conductivity of hematite due to the higher charge carrier density. Further, F:FeOOH could form p-n heterojunction in bulk where a potential barrier is built up that repels electrons but prompts holes transferring to F:FeOOH for water oxidation. What's more, the high electronegative of F^- would withdraw electron from the Fe site in FeOOH, and the enhanced positive electricity of Fe³⁺ is beneficial for adsorption of OH^- as well as enhance the conductivity of FeOOH to expedite holes transfer. As a result, the composite photoanode (F:FeOOH/Zr:Fe₂O₃) shows a 3.25-times enhanced photocurrent density comparing with α-Fe₂O₃. The special designation employs ultrathin F:FeOOH to act as both p-type semiconductor and efficient co-catalyst, avoiding redundant layer that would extend the migration distance of holes. On the top of that, the dual modification approach provides an extensive prospect for the further application of hematite.

High-performance BiVO4 photoanodes cocatalyzed with bilayer metal-organic frameworks for photoelectrochemical application

In this work, we modified a BiVO₄ photoanode with bilayer Fe-MOF and Ni-MOF as cocatalysts for the first time and obtained a highly efficient BiVO₄ composite photoanode whose photocurrent density was increased by 2.7 times. The optimized BiVO₄/Fe-MOF/Ni-MOF photoanode demonstrated a photocurrent density of 1.80 mA/cm² at 1.23 V vs. a reversible hydrogen electrode (RHE). The onset potential of the BiVO₄/Fe-MOF/Ni-MOF photoanode markedly decreased from 0.9 V to 0.69 V in comparison with the pure BiVO₄ photoanode. It is speculated that Fe-MOF and Ni-MOF led to more reactive oxygen evolution sites and that the bilayer cocatalysts synergistically promoted the separation of photogenerated electron-hole pairs, which may be the influencing factor for the photoelectrochemical performance of the BiVO₄/Fe-MOF/Ni-MOF photoanode being distinctively enhanced. Thus, this work sheds some interesting new light on the construction of a high-efficiency photoanode for photoelectrochemical applications.

Emerging architecture titanium carbide (Ti3C2Tx) MXene based photocatalyst toward degradation of hazardous pollutants: Recent progress and perspectives

MXenes family has aroused marvelous consideration as a frontier photoactive candidate for solar energy transformation and environmental remediation. 2D Ti₃C₂ exhibit a unique layered microstructure, large surface functional groups (-F, -OH, -O), substantial sorption selectivity, superior reduction efficiency, and electrical conductivity. Electronically conductive Ti₃C₂T_x with tunable energy band gap (0.92-1.75eV) makes it one of the most potential photoactive materials for photodegradation. The present review paper aims to design cost-effective heterojunctions and Schottky junctions of Ti₃C₂ with transition metal oxides, sulfides, g-C₃N₄, and other organic frameworks. The discussion mainly involves different aspects related to its tunable electronic structure, stability problems, and surface morphology control. In addition, the advantages of Ti₃C₂ in fabricating highly efficient Ti₃C₂ based catalytic junctions exhibiting suppressed charge carrier recombination are discussed with particular emphasis on their adsorption and redox properties for the removal of toxic dyes, heavy metal ions, and various pharmaceuticals. Finally, current challenges and research directions are outlined and prospected for the future development of Ti₃C₂ based photocatalytic systems.

Enhanced surface kinetics and charge transfer of BiVO4 photoanode by Rh2O3 cocatalyst loading for boosted solar water oxidation

The Rh 2 O 3 /BiVO 4 composite photoanode exhibits enhanced surface reaction kinetics and charge transfer efficiency, enabling a photocurrent density of ca. 3.5 mA/cm 2 at 1.23 V (vs. RHE), which is about 3.89 times higher than that of the pristine BiVO 4 , with a lower onset potential of 0.29 V (vs. RHE).

Boosting photoelectrochemical activity of bismuth vanadate by implanting oxygen-vacancy-rich cobalt (oxy)hydroxide

Surface charge recombination is regarded as a detrimental factor that severely downgrades the photoelectrochemical (PEC) performance of bismuth vanadate (BiVO₄). In this work, we demonstrate defect-rich cobalt (oxy)hydroxides (Co(O)OH) as an excellent cocatalyst nanolayer sheathed on BiVO₄ to substantially improve the PEC water oxidation activity. The self-transformation of metal-organic framework produces an ultrathin Co(O)OH layer rich in oxygen vacancies, which could serve as a powerful hole extraction engine to promote the charge transfer/separation efficiency as well as an excellent oxygen evolution reaction catalyst to accelerate the surface water oxidation kinetics. As a result, the BiVO₄/Co(O)OH hybrid photoanode achieves remarkably inhibited surface charge recombination and presents a prominent photocurrent density of 4.2 mA cm^-2 at 1.23 V vs. RHE, which is around 2.6-fold higher than that of the pristine BiVO₄. Moreover, the Co(O)OH cocatalyst nanolayer significantly reduces the onset potential of BiVO₄ photoanodes by 200 mV. This work provides a versatile strategy for rationally preparing oxygen-vacancy-rich cocatalysts on various photoanodes toward high-efficient PEC water oxidation.

Crystal phase engineering boosted photo-electrochemical kinetics of CoSe2 for oxygen evolution catalysis

Crystal phase is an important parameter that can determine the electronic structure and catalytic properties of catalysts. In this work, we report the crystal phase dependent photo- and electrocatalytic oxygen evolution reaction (OER) performance of CoSe₂. In electrocatalytic reaction, we firstly found that CoSe₂ with orthorhombic phase (o-CoSe₂) showed a higher OER performance than that of CoSe₂ with cubic phase (c-CoSe₂). In the further exploration of photocatalytic application using Fe₂O₃ as light harvester and CoSe₂ as cocatalysts, o-CoSe₂/Fe₂O₃ can realize the qualitative changes of photocatalytic oxygen evolution performance from "0″ to "1". As contrast, c-CoSe₂/Fe₂O₃ cannot work in photocatalytic oxygen evolution process under the same condition. Experimental and theoretical analysis uncover that, the key factor leading to the crystal phase-dependent performance is the decreased activation barrier of H₂O on o-CoSe₂ surface. This work opens up an opportunity of correlating the CoSe₂ crystal phase with performance in OER.

Direct Z-scheme SiNWs@Co3O4 photocathode with a cocatalyst of sludge-derived carbon quantum dots for efficient photoelectrochemical hydrogen production

Solar driven photoelectrochemical (PEC) hydrogen production has attracted considerable attention, but the design of highly efficient, robust and low-cost photocathode still remains a significant challenge. Herein, we report a novel SiNWs@Co₃O₄Z-scheme heterojunction photocathode with carbon quantum dots eco-friendly derived from sludge (SCQDs) as the co-catalyst. The photocathode not only leads to effective separation of electron-hole pair, lower transmission resistance, and longer lifetime of charge carriers, but also elevates the stability by preventing direct contact between the SiNWs and the electrolyte as well as the self-oxidation. Simultaneously, the excellent electron transport properties of the SCQDs further improved the PEC performance. Correspondingly, a maximum current density of 14.88 mA·cm^-2 was obtained at -0.67 V with the applied bias photon-to-current efficiency (ABPE) achieving 8.4% under visible light irradiations at pH = 7. This work provides a promising scheme for Si-based photocathodes for PEC hydrogen production with a high performance, reliable stability, and low-cost.

Rational construction of Ni(OH)2 nanoparticles on covalent triazine-based framework for artificial CO2 reduction

Artificial photoreduction of CO₂ to chemical fuel is an intriguing and reliable strategy to tackle the issues of energy crisis and climate change simultaneously. In the present study, we rationally constructed a Ni(OH)₂-modified covalent triazine-based framework (CTF-1) composites to serve as cocatalyst ensemble for superior photoreduction of CO₂. In particular, the optimal Ni(OH)₂-CTF-1 composites (loading ratio at 0.5 wt%) exhibited superior photocatalytic activity, which surpassed the bare CTF-1 by 33 times when irradiated by visible light. The mechanism for the enhancement was systematically investigated based on various instrumental analyses. The origin of the superior activity was attributable to the enhanced CO₂ capture, more robust visible-light response, and improved charge carrier separation/transfer. This study offers an innovative pathway for the fabrication of noble-metal-free cocatalysts on CTF semiconductors and deepens the understanding of photocatalytic CO₂ reduction.

Controlling the coordination environment of Co atoms derived from Co/ZIF-8 for boosting photocatalytic H2 evolution of CdS

Regulating the coordination environment of metal-N_x species by replacing N with low electronegativity atoms is an approach of tuning the electrocatalytic performance of metal-based sites. However, such effects on the enhancement of photocatalytic H₂ evolution over semiconductors are not discussed yet. Herein, we designed and prepared Co-based cocatalysts with controlled coordination environment via calcination Co/ZIF-8 loaded with triphenylphosphine followed by a sulfurization treatment. It was then used as cocatalyst to modify CdS. The effects of the coordination environment of Co atoms on the H₂ evolution activity of CdS were discussed. The obtained Co was co-stabilized by N, P, and S atoms and embedded in graphitic carbon (denoted as Co-N_xPS/C). Experimental results indicated that the Co-N_xPS/C exhibited high activity in enhancing H₂ evolution of CdS with a value of 1260 μmol after 5 h irradiation. The simultaneous replacement of N with P and S atoms in N-stabilized Co embedded in carbon could enhance light harvesting, accelerate the transfer of photogenerated electrons from CdS to carbon with increased electrons accumulation ability and conductivity, improve charge separation efficiency, and enhance proton reduction kinetics. It is believed that the results of this study could promote the development of other high performance MOF-derived atomically dispersed cocatalysts to increase photocatalytic H₂ evolution.

Non-precious molybdenum nanospheres as a novel cocatalyst for full-spectrum-driven photocatalytic CO2 reforming to CH4

Photocatalytic CO₂ reforming is considered to be an effective method for clean, low-cost, and environmentally friendly reduction and conversion of CO₂ into hydrocarbon fuels by utilizing solar energy. However, the low separation efficiency of charge carriers and deficient reactive sites have severely hampered the efficiency of the photocatalytic CO₂ reforming process. Therefore, cocatalysts are usually loaded onto the surface of semiconductor photocatalysts to reduce the recombination of charge carriers and accelerate the rates of surface reactions. Herein, molybdenum (Mo) nanospheres are proposed as a novel non-precious cocatalyst to enhance the photocatalytic CO₂ reforming of g-C₃N₄ significantly. The Mo nanospheres boost the adsorption of CO₂ and activate the surface CO₂via a photothermal effect. The time-resolved fluorescence decay spectra reveals that the lifetime of photo-induced charge carriers is prolonged by the Mo nanospheres, which guarantees the migration of charge carriers from g-C₃N₄ to Mo nanospheres. Unexpectedly, Mo loaded g-C₃N₄ can effectively utilize a wide spectral range from UV to near-infrared region (NIR, up to 800 nm). These findings highlight the potential of Mo nanospheres as a novel cocatalyst for photocatalytic CO₂ reforming to CH₄.

Semi-pilot scale production of biodiesel from waste frying oil by genetically improved fungal lipases

This paper addresses the issue of combining the usage of waste frying oil (WFO), as a feedstock, and a lipase produced in solid-state fermentation (SSF), as a biocatalyst, for semi-pilot scale production of biodiesel as fatty acid methyl esters (FAME). Two fungal mutants namely; Rhizopus stolonifer 1aNRC11 mutant F (1F) and Aspergillus tamarii NDA03a mutant G (3G) were used as a cocatalyst. The two mutants were cultivated separately by SSF in a tray bioreactor. The dried fermented solid of 1F and 3G mutants were used in a ratio of 3:1, respectively, for WFO transesterification. Optimization of several semi-pilot process stages including SSF and WFO transesterification reaction conditions resulted in 92.3% conversion of WFO to FAME. This FAME yield was obtained after 48 h using 10% cocatalyst (w/w of WFO), 10% water (w/w of WFO) and 3:1 methanol/ WFO molar ratio at 30 °C and 250 rpm. A preliminary economic evaluation of produced biodiesel price (190 $/Ton) is less than half the price of petroleum diesel in Egypt (401$/Ton) and is about 40.3% the price of biodiesel produced using a pure enzyme, which is a promising result. This strategy makes the biodiesel synthesis process greener, economical and sustainable.

Effect of L-cysteine on the oxidation of cyclohexane catalyzed by manganeseporphyrin

Effect of L-cysteine as the cocatalyst on the oxidation of cyclohexane by tert-butylhydroperoxide (TBHP) catalyzed by manganese tetraphenylporphyrin (MnTPP) has been investigated. The results showed that L-cysteine could moderately improve the catalytic activity of MnTPP and significantly increase the selectivity of cyclohexanol. Different from imidazole and pyridine, the L-cysteine may perform dual roles in the catalytic oxidation of cyclohexane. Besides as the axial ligand for MnTPP, the L-cysteine could also react with cyclohexyl peroxide formed as the intermediate to produce alcohol as the main product.