Efficient Cocatalyst Research Articles

Acceptorless Photocatalytic Dehydrogenation of Furfuryl Alcohol (FOL) to Furfural (FAL) and Furoic Acid (FA) over Ti3 C2 Tx /CdS under Visible Light.

Acceptorless photocatalytic dehydrogenation is not only a promising alternative to photocatalytic water splitting for hydrogen generation but also provides a green and sustainable strategy for the synthesis of value-added organic compounds. In this work, Ti3 C2 Tx /CdS nanocomposites were obtained by self-assembly of hexagonal CdS in the presence of preformed Ti3 C2 Tx nanosheets, which serves as a photocatalyst for acceptorless dehydrogenation of biomass-derived furfuryl alcohol (FOL) to furfural (FAL) and furoic acid (FA) in neutral and alkaline medium respectively, with simultaneous generation of stoichiometric hydrogen under visible light. Ti3 C2 Tx MXene acts as an efficient cocatalyst for the photocatalytic dehydrogenation of FOL over CdS, with an optimum performance achieved over 0.50 wt% Ti3 C2 Tx /CdS nanocomposite. This study provides an economic and sustainable strategy for the simultaneous valorization of biomass-derived FOL to produce FAL and FA as well as the production of clean energy hydrogen under mild condition based on noble metal-free semiconductor-based photocatalysts.

MOF-mediated fabrication of coralloid Ni2P@CdS for enhanced visible-light hydrogen evolution

Ni2P is an efficient cocatalyst to improve the photoelectric properties of CdS. In consideration of this, we designed a coralloid Ni2P@CdS photocatalyst (C-Ni2P@CdS) via a MOF-mediated tandem pyrolysis strategy for enhanced photocatalytic hydrogen evolution. Benefiting from the unique synergistic effect between coralloid Ni2P and CdS, C-Ni2P@CdS shown a high photocatalytic H2 production rate of 28 391 μmol h−1 g−1, nearly 11 times higher than CdS. Compared with CdS, the absorption intensity of C-Ni2P@CdS was drastically extended in the visible-light region (λ > 540 nm). Meanwhile, PL spectra, EPR and photoelectric responsiveness etc. were further employed to study the synergistic effect between Ni2P and CdS. From Density Functional Theory (DFT), strong electronic coupling effect induced electrons to accumulate on adsorbed H2O and the most energetically favorable configuration indicated that Ni-P bridges were the active sites for water dissociation. Lastly, a viable mechanism of C-Ni2P@CdS heterojunction for photocatalytic hydrogen evolution was proposed.

A sustainable molybdenum oxysulphide-cobalt phosphate photocatalyst for effectual solar-driven water splitting

IntroductionHydrogen is considered as a clean alternative green energy future fuel. Since the Honda-Fujishima effect for photoelectrochemical water splitting is known, there has been a substantial boost in this field. Numerous photocatalysts based on metals, semiconductors, and organic-inorganic hybrid-systems have been proposed. Several factors limit their efficiency, e.g., a stable PEC-WS setup, absorbing visible light, well-aligned band energy for charge transfer, electrons and holes, and their separation to avoid recombination and limited water redox reactions. Metallic doping and impregnation of stable and efficient co-catalysts such as Pt, Ag, and Au showed enhanced PEC-WS. We used Cobalt-based co-catalyst with molybdenum oxysulfide photocatalyst for effectual solar-driven water splitting. ObjectivesTo develop photocatalysts for efficient PEC processes capable of absorbing sufficient visible light, good band energy for effective charge transfer, inexpensive, significant solar-to-chemical energy conversion efficiencies. Above all, it is developing such PEC-WS systems that will be commercially viable for renewable energy resources. MethodsWe prepared Molybdenum oxysulphide-cobalt phosphate photocatalyst for PEC-WS through a facile hydrothermal route using ammonium heptamolybdate, thiourea, and metallic Cobalt precursors. ResultsAn effectual photocatalyst is produced for solar-driven water splitting. The conformal morphology of MoOxSy-CoPi nanoflowers is a significant feature, as observed under FE-SEM and HR-TEM. XRD confirmed the degree of purity and orthorhombic crystal structure of MoOxSy-CoPi. EDX and XPS identify the elemental compositions and corresponding oxidation states of each atom. A 2.44 eV band-gap energy is calculated for MoOxSy-CoPi from the diffused reflectance spectrum. Photo- Electrochemical Studies (PEC) under 1-SUN solar irradiation revealed 7-8 folds enhanced photocurrent (∼ 3.5 mA/cm2) generated from MoOxSy-CoPi/FTO in comparison to Co-PI/FTO (∼ 0.5 mA/cm2) and MoOxSy-/FTO respectively, within 0.5 M Na2SO4 electrolyte (@pH=7) and standard three electrodes electrochemical cell. ConclusionOur results showed MoOxSy-CoPi as promising photocatalyst material for improved solar-driven photoelectrochemical water splitting system.

Triple-layer ITO/BiVO4/Fe2TiO5 heterojunction photoanode coated with iron silicate for highly efficient solar water splitting

Solar water splitting as a promising way to convert solar energy into hydrogen energy has been largely limited by the low efficiency of photoanodes in photoelectrochemical water oxidation. In this work, through deliberately employing a indium tin oxide (ITO) underlayer as an electron transport layer (ETL) and a Fe2TiO5 overlayer as a hole transport layer (HTL), a novel triple-layer ITO/BiVO4/Fe2TiO5 heterojunction photoanode was prepared by solution-processed sequential deposition. Owing to the unique ETL/BiVO4/HTL heterojunction structure, the photocurrent density at 1.23 VRHE was significantly increased from 1.70 mA/cm2 for the pristine BiVO4 photoanode to 4.60 mA/cm2 for the ITO/BiVO4/Fe2TiO5 photoanode. After iron silicate (Fe-Sil) was deposited as a new and efficient cocatalyst, the resultant quaternary ITO/BiVO4/Fe2TiO5/Fe-Sil photoanode achieved an extremely high photocurrent density of 6.19 mA/cm2 and an ABPE value as high as 2.55%, indicating an outstanding performance toward solar water oxidation. The high performance of the quaternary ITO/BiVO4/Fe2TiO5/Fe-Sil photoanode may be attributed to the desired ETL/BiVO4/HTL heterojunction structure in combination with the utilization of the Fe-Sil as an efficient oxygen evolution cocatalyst.

2D bimetallic RuNi alloy Co-catalysts remarkably enhanced the photocatalytic H2 evolution performance of g-C3N4 nanosheets

The development of Pt-free co-catalysts matched with photocatalysts is one of the key technologies to improve the photocatalytic hydrogen production performance. Herein, the bimetallic RuNi alloys with a 2D structure are reported as a co-catalyst of g-C3N4 nanosheets for the first time. Its 2D structure can be well-matched with the 2D g-C3N4 nanosheets to form a composite photocatalyst with close contact. On the one hand, it is beneficial to reduce the transfer barrier of photogenerated electrons, and on the other hand, it can provide much more reaction sites for photocatalytic hydrogen production. Besides, the synergistic effect between Ru and Ni metals in the 2D bimetallic RuNi alloys makes it exhibit better co-catalytic performance than that of Pt. The RuNi/g-C3N4 photocatalyst with about 2.3% Ru contents shows a hydrogen production performance of up to 35,100 umol/g/h under simulated sunlight irradiation, which is more than twice that of the Pt/g-C3N4 photocatalyst with the same noble metal contents. The theoretical results by DFT calculation verify the experimental results and show that the 2D RuNi alloys have better performance of adsorbing H atoms and desorbing hydrogen. This work provides new insight for the development of efficient Pt-free metal cocatalysts and makes a significant step toward the development of co-catalyst with 2D structure for photocatalytic hydrogen evolution.

Bi4O5Br2 anchored on Ti3C2 MXene with ohmic heterojunction in photocatalytic NH3 production: Insights from combined experimental and theoretical calculations

Nitrogen-to-ammonia conversion under mild conditions offers a tremendous prospect as a sustainable technology for synthesizing ammonia (NH3) in the future. In this study, we elaborately designed Bi4O5Br2/Ti3C2 heterojunction combined with electrostatic adsorption with in-situ growth to form a photocatalyst with a 2D/2D structure. This unique structure substantially improved the exposure of active edge sites for photocatalytic dinitrogen reduction reaction. Notably, Ti3C2 MXene acted as an efficient cocatalyst for the conversion of N2 to NH3 of Bi4O5Br2/Ti3C2 with a yield of 277.74 μmol g−1h−1 without the use of a sacrificial agent; this yield was five times higher than that of Bi4O5Br2. Density functional theory calculations demonstrated that the ohmic contact was at the Bi4O5Br2/Ti3C2 interface. The ohmic heterojunction could expedite the separation of spatial carriers and extraction of photoexcited charge carriers, which had outstanding reducibility to cleavage the N≡N bond. This work provides a novel strategy for designing highly efficient Bi4O5Br2-based photocatalysts through the integration of multifunctional materials. This work also offers guidance for implementing high-performance nitrogen-to-ammonia conversion by introducing interfacial modifiers.

Inactivation of pathogens by visible light photocatalysis with nitrogen-doped TiO2 and tourmaline-nitrogen co-doped TiO2

• Effective photo-inactivation of bacteria, mycobacteria, and fungi were achieved. • Tourmaline acts as an efficient co-catalyst improved N-TiO 2 for photo-inactivation. • Key variables affecting S. aureus photo-inactivation were systemically evaluated. • Inactivation kinetics of S. aureus are well described by LMH model. • Hydroxyl radicals are the major radicals govern the photo-inactivation processes. Four types of pathogens, namely, Staphylococcus aureus ( S. aureus , gram-positive bacteria), Escherichia coli ( E. coli , gram-negative bacteria), Mycobacterium avium ( M. avium, mycobacteria), and Candida albicans ( C. albicans , fungi), are common microorganisms that cause serious human health issues. However, searching for an efficient material for inactivating pathogens via visible light driven photocatalysts remains a challenge. An attempt was made to compare the photocatalytic performance using nano-sized nitrogen-doped titanium oxide (N-TiO 2 ) and tourmaline-nitrogen-co-doped titanium oxide (T-N-TiO 2 ) for inactivation of pathogens under visible light irradiation. S. aureus was used to compare the photocatalytic inactivation performance of N-TiO 2 and T-N-TiO 2 . The findings showed that photocatalyst dosage, initial microbial concentration, and visible light intensity are the key factors affecting photocatalytic inactivation process for both photocatalysts. A 2-log-inactivation of S. aureus under 7.25 mW/cm 2 visible light irradiation via T-N-TiO 2 was achieved within 3 h, which is shorter than the inactivation via N-TiO 2 (4 h). TEM observations had proved that both visible-light-induced photocatalysis could cause severe damage to the cell membrane. The results of electron paramagnetic resonance also indicated that more hydroxyl radicals generated in the T-N-TiO 2 photo-inactivation system allowed a better inactivation performance of the visible-light-induced T-N-TiO 2 . This is the first work exploring that Light-responsive Modified Hom’s model (LHM) is able to simulate photocatalytic inactivation of S. aureus . T-N-TiO 2 composite was firstly evaluated for its efficacy of photocatalytic inaction of S. aureus , E. coli, and M. avium , and an increasing order of time was required for complete inactivation as follows: S. aureus < E. coli < M. avium < C. albicans. We have found that the inactivation efficiency of tested pathogens using T-N-TiO 2 is the highest as compared with literature works. Overall, T-N-TiO 2 exhibits a better inactivation efficiency than that of N-TiO 2 in all the tested pathogens.

CdS Nanorods Anchored with Crystalline FeP Nanoparticles for Efficient Photocatalytic Formic Acid Dehydrogenation.

Photocatalytic dehydrogenation of formic acid is a promising strategy for H2 generation. In this work, we report the use of crystalline iron phosphide (FeP) nanoparticles as an efficient and robust cocatalyst on CdS nanorods (FeP@CdS) for highly efficient photocatalytic formic acid dehydrogenation. The optimal H2 evolution rate can reach ∼556 μmol·h-1 at pH 3.5, which is more than 37 times higher than that of bare CdS. Moreover, the photocatalyst demonstrates excellent stability; no significant decrease of the catalytic activity was observed during continuous testing for more than four days. The apparent quantum yield is ∼54% at 420 nm, which is among the highest values obtained using noble-metal-free photocatalysts for formic acid dehydrogenation. This work provides a novel strategy for designing highly efficient and economically viable photocatalysts for formic acid dehydrogenation.

Activation Strategy of WS2 as an Efficient Photocatalytic Hydrogen Evolution Cocatalyst through Co2+ Doping to Adjust the Highly Exposed Active (100) Facet

As an effective method to improve the surface catalytic activity of catalysts, crystal plane engineering has become a research hot spot in recent years. Doping regulation of the highly exposed facet with low surface energy is helpful to expand their applications in the field of photocatalysis. Therefore, low concentration transition metal ions (Co2+) in the high exposure surface (100) of WS2 by one‐pot hydrothermal method are doped. Moreover, density functional theory (DFT) calculation shows that after Co2+ in WS2 (100) crystal replaces W4+, the surface charge is rearranged, and the local charge near Co2+ is enhanced, which accelerates the electron transfer rate, makes the electron transfer rapidly to (100) facet through the secondary transfer process, and finally promotes proton reduction. Therefore, the hydrogen production efficiency of 7% (Co–WS2)/Cd0.4Zn0.6S (CZS) Schottky junction (21 000 μmol g−1 h−1) is 9.3 times and 1.3 times higher than that of CZS (2265 μmol g−1 h−1) and 7% WS2/CZS heterojunction (17 000 μmol g−1 h−1). This study has certain reference and guiding significance for the study of new cocatalysts, not only on pristine semiconductor but also for semiconductor‐based hybrid structures.

Hydrogen bonded metal–organic supramolecule functionalized BiVO4 photoanode for enhanced water oxidation efficiency

Hydrogen bonded metal–organic supramolecules are a new family of cocatalysts for high-efficiency water oxidation photoanodes owing to their suitable electrical conductivity. We herein designed a calix[4]resorcinarene-based metal–organic supramolecular system with rich hydrogen bonds, namely [Cu2L(H2O)2]∙3DMF (L = calix[4]resorcinarene-based ligand and DMF = N,N’-dimethylformamide) or Cu2L. Then, the hydrogen bonded metal–organic supramolecular system was applied as a cocatalyst in BiVO4 nanoplate photoanode for water oxidation reaction. Photoelectrochemical and electrochemical analysis demonstrated that the obtained Cu2L-modified BiVO4 photoanode showed greatly enhanced water oxidation efficiency, which was about three times higher than bare BiVO4 nanoplates. In addition, photoelectrochemical activity was well maintained within three hours. Cu2L as an efficient cocatalyst can promote the holes on the surface of the photoanode to participate in the oxygen evolution reaction, thus improving the performance of the photoanode. This work presents a feasible strategy by using the hydrogen bonded metal–organic supramolecular system to functionalize photoanodes for enhanced water oxidation efficiency.

A novel noble-metal-free binary and ternary In2S3 photocatalyst with WC and “W-Mo auxiliary pairs” for highly-efficient visible-light hydrogen evolution

Herein, noble-metal-free In2S3-WC and In2S3-based photocatalysts with dual cocatalysts of flower-like MoS2 and bulk WC were synthesized through a facile solvothermal reaction. Electrochemical results indicated WC increased the interface conductance of photocatalyst and boosted the transference of photogenerated carriers. The optimal In2S3-WC show a hydrogen production rate of 128.11 μmol·h−1·g−1, which is around 6 times higher than In2S3-1%Pt (20.73 μmol·h−1·g−1). The above results demonstrate commercial WC has a crucial impact of replacing precious metal and separating carriers. Morphology characterization exhibited hydrangea In2S3 and flower-like MoS2 were attached to bulk WC. Gratifyingly, photocurrent, impedance and photoluminescence results demonstrated MoS2 further effectively separated the photogenerated carriers. Remarkably, the higher hydrogen generation rate of 390.52 μmol·h−1·g−1 obtained by the optimal ternary In2S3-WC-MoS2 composite was around 3 and 18 times higher than the optimal In2S3-WC and In2S3-1% Pt. The photocatalytic results demonstrated that "W-Mo auxiliary pairs" was a great efficient synergistic cocatalyst for In2S3 to increase active sites and improve e--h+ pairs separation for H2 generation. Furthermore, a probable reaction mechanism of the enhanced photocatalytic H2 generation was also proposed. This presented research provides an effective concept to design novel and efficient noble-metal-free photocatalyst with "W-Mo auxiliary pairs" for prominent H2 generation activity.

Facile preparation of metallic 1T phase molybdenum selenide as cocatalyst coupled with graphitic carbon nitride for enhanced photocatalytic H2 production

Low-cost, highly active and efficient alternative co-catalysts that can replace precious metals such as Au and Pt are urgently needed for photocatalytic hydrogen evolution reaction (HER). Herein, we show that 1T phase MoSe2 can act as the co-catalyst in the 1T-MoSe2/g-C3N4 composites and we synthesize this composite by a one-step hydrothermal method to promote photocatalytic H2 generation. Our prepared 1T-MoSe2/g-C3N4 composite exhibits highly enhanced photocatalytic H2 production compared to that of g-C3N4 nanosheets (NSs) only. The 7 wt%-1T-MoSe2/g-C3N4 composite presents a considerably improved photocatalytic HER rate (6.95 mmol·h−1·g−1), approximately 90 times greater than that of pure g-C3N4 (0.07 mmol·h−1 g−1). Moreover, under illumination at λ = 370 nm, the apparent quantum efficiency (AQE) of the 7 wt%-1T-MoSe2/g-C3N4 composite reaches 14.0%. Furthermore, the 1T-MoSe2/g-C3N4 composites still maintain outstanding photocatalytic HER stability.

In situ formation of amorphous Fe-based bimetallic hydroxides from metal-organic frameworks as efficient oxygen evolution catalysts

Available online 5 April 2021Oxygen evolution from water driven by electrocatalysis or photocatalysis poses a significant challenge as it requires the use of efficient electro-/photo-catalysts to drive the four-electron oxygen evolution reaction (OER). Herein, we report the development of an effective strategy for the in situ chemical transformation of Fe-based bimetallic MIL-88 metal-organic frameworks (MOFs) into corresponding bimetallic hydroxides, which are composed of amorphous ultrasmall nanoparticles and afford an abundance of catalytically active sites. Optimized MOF-derived NiFe-OH-0.75 catalyst coated on glassy carbon electrodes achieved a current density of 10 mA cm−2 in the electrocatalytic OER with a small overpotential of 270 mV, which could be decreased to 235 mV when loading the catalysts on a nickel foam substrate. Moreover, these MOF-derived Fe-based bimetallic hydroxides can be used as efficient cocatalysts when combined with suitable photosensitizers for photocatalytic water oxidation.

Surface assembly of cobalt species for simultaneous acceleration of interfacial charge separation and catalytic reactions on Cd0.9Zn0.1S photocatalyst

Although photocatalytic water splitting has excellent potential for converting solar energy into chemical energy, the challenging charge separation process and sluggish surface catalytic reactions significantly limit progress in solar energy conversion using semiconductor photocatalysts. Herein, we demonstrate a feasible strategy involving the surface assembly of cobalt oxide species (CoOx) on a visible-light-responsive Cd0.9Zn0.1S (CZS) photocatalyst to fabricate a hierarchical CZS@CoOx heterostructure. The unique hierarchical structure effectively accelerates the directional transfer of photogenerated charges, reducing charge recombination through the smooth interfacial heterojunction between CZS and CoOx, as evidenced by photoluminescence (PL) spectroscopy and various electrochemical characterizations. The surface cobalt species on the CZS material also act as efficient cocatalysts for photocatalytic hydrogen production, with activity even higher than that of noble metals. The well-defined CZS@CoOx heterostructure not only enhances the interfacial separation of photoinduced charges, but also improves surface catalytic reactions. This leads to superior photocatalytic performances, with an apparent quantum efficiency of 20% at 420 nm for visible-light-driven hydrogen generation, which is one of the highest quantum efficiencies measured among noble-metal-free photocatalysts. Our work presents a potential pathway for controlling complex charge separation and catalytic reaction processes in photocatalysis, guiding the practical development of artificial photocatalysts for successful transformation of solar to chemical energy.

Independent Cr2O3 functions as efficient cocatalyst on the crystal facets engineered TiO2 for photocatalytic CO2 reduction

Implanting cocatalysts on semiconductor photocatalysts is considered as an essential strategy to promote reaction activity. However, the development of highly efficient cocatalysts remains challenging. In the present work, we construct independent Cr2O3 as an efficient cocatalyst on the crystal facets engineered TiO2 for photocatalytic CO2 reduction for the first time. Moreover, a combined strategy of crystal facets engineering of TiO2 and loading of Cr2O3 cocatalyst is adopted to further promote the charge carriers’ separation/transfer. In comparison with the cocatalyst-free TiO2 without facets engineering, 2HF-TiO2/0.2Cr2O3 exhibits near 30-fold enhancement on the CO2 conversion efficiency. The enhanced photocatalytic activity is attributed to the maximal synergy of crystal facets engineering and cocatalyst loading for well-matched CO2 reduction half-reaction and H2O oxidation half-reaction. These findings not only provide new insights for understanding the role of Cr2O3 in photocatalytic systems but also may shed light on the design of photocatalysts from the perspective of overall photocatalytic CO2 reduction.

Metal-free tellurene cocatalyst with tunable bandgap for enhanced photocatalytic hydrogen production

The discovery of metal-free elemental cocatalysts has spurred dramatic advances in the field of photocatalysis. Bandgap engineering has always been used as an effective approach to make these cocatalysts form favorable band alignment with photocatalysts. Here, we develop metal-free tellurene (Te) with largely tunable bandgap as a highly efficient cocatalyst and investigate its thickness-dependent catalytic activity. Our experimental and theoretical studies reveal that the increased reduction potential of conduction band together with the decreased thickness, abundant active sites, and high charge mobility of Te, as well as the strong electronic coupling effects between Te and metal sulfides enable the enhanced photocatalytic hydrogen evolution rate and high quantum efficiency of 11.4% under the light illumination with the wavelength of 420 nm. This work enriches our understanding of the structure–activity correlations for Te and opens a path for solar energy harvesting from artificial photosynthesis by robust and cost-effective photocatalysts.

In Situ Synthesis of Mo2C Nanoparticles on Graphene Nanosheets for Enhanced Photocatalytic H2-Production Activity of TiO2

Molybdenum carbide (Mo₂C) has been proven to be the most promising candidate for the H₂-evolution cocatalyst due to the similar H⁺-adsorption ability to Pt. However, owing to its limited electrical conductivity, the Mo₂C-modified photocatalysts usually exhibit a low H₂-evolution performance. Considering the perfect electron mobility of graphene nanosheets, in this article, Mo₂C nanoparticles (ca. 5 nm) were in-situ and evenly grown on the reduced graphene oxide (rGO) to prepare the graphene-modified Mo₂C (rGO-Mo₂C) nanoparticles to improve the photocatalytic hydrogen-generation rate of TiO₂. Herein, the rGO-Mo₂C is obtained by the direct calcination of graphene oxide (GO) as the carbon source and (NH₄)₆Mo₇O₂₄ at 800 °C, which is further coupled with the TiO₂ to synthesize the efficient TiO₂/rGO-Mo₂C photocatalyst. The greatest hydrogen-generation activity of TiO₂/rGO-Mo₂C achieved 880 μmol h–¹ g–¹ (AQE = 2.64%), which was 5.5 and 88 times higher than that of TiO₂/rGO and TiO₂, respectively. The boosted performance of TiO₂/rGO-Mo₂C can be attributed to the synergetic action that the rGO nanosheets can act as electron media to promote the photoelectron transfer, and the Mo₂C nanoparticles can serve as active centers to improve the interfacial hydrogen-generation reaction. This work can provide a new synthesis strategy for the design of efficient cocatalysts for potential applications.

Synergism of tellurium-rich structure and amorphization of NiTe1+x nanodots for efficient photocatalytic H2-evolution of TiO2

The exploitation and design of novel low-cost cocatalysts with rich H2-evolution active centers is quite crucial for markedly promoting the photocatalytic activity. Herein, tellurium-rich amorphous NiTe1+x nanodots as a novel and robust H2-generation cocatalyst were ingeniously loaded onto the TiO2 to greatly improve its photocatalytic H2-evoluton performance via a synergistic strategy of tellurium-rich structure and amorphization, with an aim of maximally exposing more H2-evolution site of tellurium atoms. In this case, tellurium-rich amorphous NiTe1+x nanodots were very small (0.3–1 nm) and uniformly modified onto the TiO2 by the facile photoinduced synthesis route, and the resultant a-NiTe1+x/TiO2(0.5 wt%) achieves the highest H2-evolution rate (3302 μmol h−1 g−1, AQE = 15.8 %). The superior activity can be attributed to the successful deposition of tellurium-rich amorphous NiTe1+x nanodots, which can not only efficiently enhance the photoinduced electron migrate from TiO2, but also supply abundant active tellurium sites to accelerate the interfacial H2-evolution process. Significantly, the tellurium-rich a-NiTe1+x can also be utilized as the universal cocatalyst. This research may provide new avenues to develop efficient and low-cost cocatalysts with abundant enriched active-sites for high performance photocatalysts.

Dual-phase metal nitrides as highly efficient co-catalysts for photocatalytic hydrogen evolution

Low solar-to-fuel conversion in conventional semiconductor-based photocatalysts limits their commercial applications. Searching for highly efficient cost-effective co-catalysts is desirable for the development of artificial photosynthesis systems. In this work, we report a simple yet efficient electrostatic self-assembly process to synthesize one-dimensional Co4N-WNx-CdS composites for visible light-driven hydrogen evolution in pure water. Biphasic transition metal nitrides Co4N-WNx with high conductivity and enriched active sites leads to multi-level electrons transfer and lower over-potential for hydrogen production. Co4N-WNx-CdS composite, with optimized wt%, exhibits the highest rate of photocatalytic hydrogen evolution (14.42 mmol g−1h−1) under vacuum condition. This rate is ~ 8 times higher than that of the Pt-CdS composite (1.78 mmol g−1h−1).

Integrating heteromixtured Cu2O/CuO photocathode interface through a hydrogen treatment for photoelectrochemical hydrogen evolution reaction

Mono and divalent copper oxide (Cu2O and CuO) has been considered as a potential semiconductor photocathode with capability for hydrogen (H2) production. The use of one-dimensional (1D) nanostructures as photocathode is desirable for the photoelectrochemical water-splitting device due to the large surface areas, lateral carrier extraction property, and excellent light-harvesting potentiality. Accordingly, the numerous attempts to develop copper oxide heterojunctions via a bottom-up approach has been achieved, but, the resulting composites have suffered from the poor interfacial configuration. Here, we demonstrate the intimate modulation through the different ambient annealing of photocathodes could alter the nanostructure, light-harvesting, and optical bandgap. Accordingly, the Cu2O/CuO heterostructure was synthesized by in situ growth via simple electrochemical anodization of Cu foil followed by annealing in air, and then the surfaces of the heterostructure were sequentially modified by the formation of Cu(OH)2 via the post-annealing process under 4% hydrogen-argon mixed gas at 300 °C. As a result, a mild hydrogen treatment (H2@1min) was found to be effective in enhancing the PEC properties, due to the favorable formation of Cu2O/CuO/Cu(OH)2 layer, promoting the photogenerated charge collection yield; the generation of sufficient cation vacancies was closely related to the electronic conductivity and the charge-transfer yield. The TEM and XPS results confirmed that the hydrogen treatment found a slightly thin Cu(OH)2 layer was produced as an efficient co-catalyst from the inherent chemical reduction of prominent CuO phase to develop the junction of Cu2O/CuO/Cu(OH)2. Overall, the Cu2O/CuO/Cu(OH)2(H2@1min) film exhibited an obvious improvement in photocurrent density of −2.3 mA/cm2 at 0 V vs. reversible hydrogen electrode (RHE) (abbreviated as 0 VRHE) than those nanowires having −1.72 and −1.44 mA/cm2 of both Cu2O/CuO/Cu(H2@3min) and Cu2O/CuO(Air), respectively.