Highest H2 Evolution Research Articles

One-step facile synthesis and high H2-evolution activity of suspensible CdxZn1-xS nanocrystal photocatalysts in a S2-/SO32- system.

For a CdS-based photocatalyst, both the photocorrosion resistance and the rapid H2-production reaction are highly required for improving its photocatalytic H2-production performance. In this study, a facile strategy was reported to simultaneously realize an improved photocorrosion resistance and rapid interfacial H2-evolution reaction of CdxZn1-xS solid-solution photocatalysts in a sulfur-rich S2-/SO32- solution. Here, the suspensible CdxZn1-xS nanocrystal photocatalysts are prepared by a one-step co-precipitation route through the direct introduction of Zn2+/Cd2+ mixing ions in a sulfur-rich Na2S-Na2SO3 solution, and the resultant CdxZn1-xS nanocrystals (ca. 5 nm) display a suspensible structure owing to the numerous and selective adsorption of S2-/SO32- on the surface of these CdxZn1-xS nanocrystals. It is found that the bandgap structure of CdxZn1-xS (from 2.25 to 3.52 eV) nanocrystals can be easily controlled by adjusting the Cd2+/Zn2+ molar ratio. The photocatalytic experimental results suggested that the suspensible CdxZn1-xS nanocrystal photocatalysts clearly displayed an excellent photocatalytic H2-production performance, and the suspensible Cd0.6Zn0.4S nanocrystals exhibit the highest photocatalytic H2-generation performance of 717.19 μmol h-1, a value higher than that of the sole CdS (320.99 μmol h-1) and ZnS (5.89 μmol h-1) by a factor of 2.2 and 121.8 times, respectively. Based on the experimental results, a possible S2- active site-mediated mechanism accounted for the high H2-production activity of the suspensible CdxZn1-xS nanocrystals, namely the numerous adsorbed S2- ions not only function as efficient hole scavengers to rapidly consume the photogenerated holes, resulting in an improved photocorrosion resistance of suspensible CdxZn1-xS nanocrystals, but also serve as effective H+-capturing active sites to accelerate the interfacial H2-production reaction. Meanwhile, an optimum bandgap structure of suspensible CdxZn1-xS nanocrystals is also extremely required for promoting the photocatalytic H2-production activity. This research may provide advanced insights for developing stable and high-activity photocatalytic materials.

Fe4S4 Cubane Type Cluster Immobilized on a Graphene Support: A High Performance H2 Evolution Catalysis in Acidic Water

The development of alternate catalysts that utilize non-precious metal based electrode materials such as the first row transition metal complexes is an important goal for economic fuel cell design. In this direction, a new Fe4S4 cubane type cluster, [PPh4]2[Fe4S4(DMET)4] (1) (DMET = cis-1,2-dicarbomethoxyethylene dithiolate) and its composite with functionalized graphene, (1@graphene) have been synthesized and characterized. The presence of nanocrystalline structures on graphene matrix in TEM and SEM images of 1@graphene indicate that the cluster (1) has been immobilized. The composite, 1@graphene evolves H2 gas from p-toluene sulfonic acid (TsOH) in a mixture of H2O and CH3CN under ambient conditions with a significant turnover number of 3200. 1@graphene electro-catalyzes H2 evolution at Ep, −1.2 V with remarkable throughput, catalytic efficiency and stability in only H2O or in only CH3CN. The Fe4S4 cluster (1) alone electro-catalyzes hydrogen evolution at Ep, −0.75 V from TsOH in CH3CN. The X-ray crystal structure of the Fe4S4 cluster (1) (λmax, CH2Cl2, 823 nm; ε, 2200 mol−1 cm−1) shows that it is dianionic with a cumulative oxidation state of +2.5 for the iron centers and short C-S bond distances (ca., 1.712 Å & 1.727 Å) indicating the presence of sulfur based radicals.

Synergistic effect of electron-transfer mediator and interfacial catalytic active-site for the enhanced H2-evolution performance: A case study of CdS-Au photocatalyst

For noble metal cocatalyst-modified photocatalysts with a high H2-evolution performance, both of the rapid electron transfer (or electron capture) from semiconductor to cocatalyst and the following interfacial catalysis for H2 production on the cocatalyst surface are highly required. Compared with Pt-loaded photocatalyst, Au-modified sample usually shows an obviously lower H2-evolution activity due to its inefficient H2-production rate on the Au cocatalyst surface. In this study, the SCN− ions as the catalytic active sites are selectively adsorbed on the Au surface of CdS/Au photocatalysts (CdS/Au-SCN), with the aim of promoting the interfacial H2-evolution reaction on Au cocatalyst and improving the photocatalytic water-splitting efficiency of CdS/Au system. The CdS/Au-SCN photocatalysts were synthesized via a two-step process including the initial photoinduced deposition of Au nanoparticles on CdS surface and the following selective adsorption of SCN− on the Au surface by an impregnation method. It was found that the resultant CdS/Au-SCN photocatalysts exhibited obviously improved photocatalytic H2-evolution activity compared with the CdS, CdS/Au and CdS/SCN photocatalysts. Especially, the CdS/Au-SCN(0.5mM) achieved the highest photocatalytic activity (109.60μmolh−1) with an apparent quantum efficiency (QE) of 11.25%, which was clearly higher than that of CdS and CdS/Au by a factor of 2.3 and 1.5 times, respectively. The enhanced H2-evolution performance of CdS/Au-SCN can be attributed to the excellent synergistic effect of Au and SCN−, namely, the Au nanoparticle functions as an effective electron-transfer mediator for the steady capture and rapid transportation of photogenerated electrons from CdS surface, while the adsorbed SCN− serves as the interfacial catalytic active-site to effectively adsorb H+ ions from solution and promote the rapid H2-evolution reaction. The present synergistic mechanism of electron-transfer mediator and interfacial catalytic active-sites may provide some new insights for the design of highly efficient photocatalytic materials.

Amorphous WSx as an efficient cocatalyst grown on CdS nanoparticles via photochemical deposition for enhanced visible-light-driven hydrogen evolution

Development of highly active and earth-abundant cocatalysts to replace scarce noble-metals is of great importance to realize large-scale and cost-efficient photocatalytic H2 evolution reactions. Herein, we report that amorphous WSx cocatalyst grown on the CdS surface by a facile solution-based photochemical reduction method is an effective alternative for Pt cocatalyst and lead to superior photocatalytic H2 evolution performances. Under visible light irradiation (≥420nm), the optimized CdS/WSx (12%) photocatalyst achieved a high initial H2 evolution rate of 761μmolh−1, which is the 17 times faster than that of CdS alone. Notably, the WSx cocatalyst shows a nearly 5 times higher activity than that of Pt in catalyzing H2 evolution on CdS at same loading amount. An apparent quantum efficiency (AQE) of 14.7% was achieved over CdS/WSx (12%) at 420nm. Moreover, CdS/WSx(12%) photocatalyst is relatively stable for 20h H2 evolution reactions, showing the robustness of WSx cocatalyst. Based on the results of photoelectrochemical and PL measurements, it was proposed that the amorphous WSx not only can rapidly capture photogenerated electrons from excited CdS for enhancing the charge separation efficiency, but also promote the H+ reduction to H2. Considering its high activity, easy-preparation, and low cost, the amorphous WSx cocatalyst would hold great potential in designing high-performance semiconductor/WSx photocatalysts for large-scale H2 production using renewable energy sources.

One-pot construction of 1D/2D Zn1-xCdxS/D-ZnS(en)0.5 composites with perfect heterojunctions and their superior visible-light-driven photocatalytic H2 evolution

A series of well-defined 1D/2D Zn1-xCdxS/D-ZnS(en)0.5 hybrids are fabricated via an one-pot synthesis method. The resulting composites exhibit enhanced visible-light-driven photoactivities for H2 production from water in the presence of sacrificial reagents. The optimized Zn0.41Cd0.59S/D-ZnS(en)0.5 hybrid shows the extremely high H2 evolution rate of 463.6μmolH−1 per 30mg under visible light irradiation (λ>420nm), without any cocatalysts. The highest H2 production rate presents 826-fold and 24-fold enhancement compared to pristine D-ZnS(en)0.5 and CdS, respectively. The corresponding apparent quantum yield (AQY) at 440nm reaches up to 49.95%. The dramatically improved photocatalytic performance could be attributed to the effective interfacial and interior carriers separation. The former is based on the perfect Zn0.41Cd0.59S/D-ZnS(en)0.5 heterojunctions with well-matched lattice and band structure, which is obtained by collaborative optimization of composition regulation and defect mediation. While the latter is achieved by low dimension control on the basis of the unique electronic behavior in low-dimensional materials. Besides, the stability of Zn0.41Cd0.59S/D-ZnS(en)0.5 heterostructure is also investigated. Several possible causes of slight deactivation are proposed, which mainly includes the weakened interfacial contact, partial ethylenediamine (en) ligands dissociation or substitution by H2O, OH− and S2−, repair of S vacancies and partial oxidation of Cd-S bonds. It may provide theoretic guidance for further designing high-stability photocatalysts. In addition, the optimized hybrid can be used at ambient pressure and under natural sunlight illumination, and the synthesis method is facile, economic and short-period. Thus our proposed system is highly attractive for large scale energy applications.

Preparation of Ag/Ga2O3 nanofibers via electrospinning and enhanced photocatalytic hydrogen evolution

In this paper, gallium oxide (Ga2O3) was modified by in situ silver (Ag) to improve the photocatalytic activity for hydrogen (H2) evolution. The photocatalysts Ga2O3 and Ag/Ga2O3 were synthesized via electrospinning and calcination, and characterized by X-ray diffraction patterns (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscope (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS). It is observed that the 1% Ag/Ga2O3 had higher activity than that of the pure Ga2O3 for photocatalytic H2 evolution. Photoluminescence spectra (PL) and transient photocurrent analysis indicated that the high separation efficiency of photo-generated carriers of Ag/Ga2O3 resulted in the high photocatalytic H2 evolution.

In-situ photo-deposition CuO1−x cluster on TiO2 for enhanced photocatalytic H2-production activity

CuO1−x cluster-modified TiO2 (CuO1−x/TiO2) photocatalysts were prepared by an in-situ photoreduction deposition of Cu on TiO2 powder support using copper acetate as a Cu source. The prepared samples without any Pt co-catalyst present an especially high photocatalytic H2-evolution activity under solar light irradiation with 5% glycerol as sacrificial agent. The optimal CuO1−x/TiO2 catalyst with only 1 wt% CuO1−x exhibits a high activity of 1725 μmol h−1 g−1 for H2 evolution, which reaches 120 times that of TiO2. The high photocatalytic activity of H2 production is attributed to the highly dispersed CuO1−x nano clusters on the surface of the TiO2. In addition, Pt/CuO1−x/TiO2 was also prepared by loading Pt on CuO1−x/TiO2 sample, and its photocatalytic hydrogen evolution activity is enhanced 1.8 times compared with that of Pt/TiO2 for overall water splitting reaction under solar light, demonstrating that a small amount CuO1−x wondrously improves the photocatalytic activity of Pt/TiO2 for overall water splitting reaction. This paper reports an economic and simple approach to prepare a photocatalyst with high hydrogen-production activity.

Anchoring ultrafine metallic and oxidized Pt nanoclusters on yolk-shell TiO2 for unprecedentedly high photocatalytic hydrogen production

We demonstrate an alkali modification process to produce highly dispersed ultrafine Pt nanoclusters with metallic Pt0 and oxidized Pt2+ species as co-catalyst anchored on nanosheet-constructed yolk-shell TiO2 (NYTiO2-Pt) acting as light harvesting reactor for highly efficient photocatalytic H2 production. Benefiting from the high surface area, highly dispersed ultrafine Pt nanoclusters (~0.6nm) with Pt0 and Pt2+ species and special nanosheet-constructed yolk-shell structure, this novel light harvesting reactor exhibits excellent performance for photocatalytic H2 production. The NYTiO2-Pt-0.5 (0.188wt% Pt) demonstrates an unprecedentedly high H2 evolution rate of 20.88mmolh−1g−1 with excellent photocatalytic stability, which is 87 times than that of NYTiO2-Pt-3.0 (0.24mmolh−1g−1, 1.88wt% Pt), and also much higher than those of other TiO2 nanostructures with the same Pt content. Such H2 evolution rate is the highest reported for photocatalytic H2 production with such a low Pt content under simulated solar light. Our strategy here suggests that via alkali modifying the photocatalysts, we can not only enhance the H2 production for solar energy conversion but also significantly decrease the noble metal content for cost saving.

High Efficiency Photocatalytic Water Splitting Using 2D α‐Fe2O3/g‐C3N4 Z‐Scheme Catalysts

Photocatalysis is the most promising method for achieving artificial photosynthesis, but a bottleneck is encountered in finding materials that could efficiently promote the water splitting reaction. The nontoxicity, low cost, and versatility of photocatalysts make them especially attractive for this application. This study demonstrates that small amounts of α‐Fe2O3 nanosheets can actively promote exfoliation of g‐C3N4, producing 2D hybrid that exhibits tight interfaces and an all‐solid‐state Z‐scheme junction. These nanostructured hybrids present a high H2 evolution rate >3 × 104 µmol g‐1 h‐1 and external quantum efficiency of 44.35% at λ = 420 nm, the highest value so far reported among the family of g‐C3N4 photocatalysts. Besides effectively suppressing the recombination of electron–hole pairs, this Z‐scheme junction also exhibits activity toward overall water splitting without any sacrificial donor. The proposed synthetic route for controlled production of 2D g‐C3N4‐based structures provides a scalable alternative toward the development of highly efficient and active photocatalysts.

Hetero-structural NiTiO3/TiO2 nanotubes for efficient photocatalytic hydrogen generation

Hetero-structural NiTiO3/TiO2 nanotubes were prepared by an in-situ reaction method, and were used as photocatalysts for hydrogen generation from water splitting. By virtue of the nanotubular morphology and the stable hetero-architecture, the prepared samples show excellent photocatalytic activity and high stability for repeated use. Especially, there appear to be an optimum NiTiO3 content of 1.77 mol.%, giving a high and stable H2 evolution rate of about 680 μmol g−1 h−1, which exceeds that of pure TiO2 nanotubes and zero-dimensional TiO2 nanoparticles by about 15 times and 55 times, respectively.

One-pot hydrothermal synthesis of CdS/NiS photocatalysts for high H2 evolution from water under visible light

The development of efficient and stable noble-metal-free photocatalysts is crucial for hydrogen evolution from water splitting as clean energy. This study reports uniform CdS/NiS spherical nanoparticles through a simple one-pot hydrothermal method with the aid of KOH. The prepared CdS/NiS composites show superior photocatalytic activities toward the water splitting under visible light. A suitable amount of KOH in the synthesis benefits to form CdS/NiS photocatalysts with the improved activity. The CdS/NiS composite including 10 mol% metal percentage of Ni exhibits the highest photocatalytic activity. The high hydrogen evolution rate of 24.37 mmol h−1 g−1 is achieved over the CdS/NiS composite photocatalyst. The CdS/NiS photocatalyst has good photocatalytic stability in the recycling uses. The present CdS/NiS as a noble-metal-free photocatalyst provides the superior visible-light driven catalytic activity for hydrogen evolution.

Cobalt Phosphide Modified Titanium Oxide Nanophotocatalysts with Significantly Enhanced Photocatalytic Hydrogen Evolution from Water Splitting.

Production of hydrogen from photocatalytic water splitting holds promise as an alternative energy source with superiority of cleanliness, environment friendliness, low price, and sustainability. Perfectly constructing the noble-metal-free and stable hybrid structure photocatalyst is quite essential; herein, for the first time the authors aim to use cobalt phosphide as the cocatalyst on titanium oxide to form a novel hybrid structure to enhance the utilization of the photoexcited electrons in redox reactions for improved photocatalytic H2 evolution activity. Thus, the achieved significantly increased photocatalytic H2 -evolution rate on the optimized CoP/TiO2 (8350 µmol h-1 g-1 ) is 11 times higher than that of the pristine TiO2 . Moreover, this work is expected to spur more insight into synthesizing such novel photofunctional systems, achieving high photocatalytic H2 evolution activity and sufficient stability for solar-to-chemical conversion and utilization.

A Sustainable Strategy for the Synthesis of Pyrochlore H4 Nb2 O7 Hollow Microspheres as Photocatalysts for Overall Water Splitting.

A facile and green process was developed for the synthesis of pyrochlore H4 Nb2 O7 hollow microspheres by using hydrothermal treatment of Sn2 Nb2 O7 hollow microspheres in aqueous 2 m HCl at 100-180 °C. The facile transformation of Sn2 Nb2 O7 into H4 Nb2 O7 is facilitated by the intrinsic ion-exchange capability of Sn2 Nb2 O7 . The resulting H4 Nb2 O7 hollow microspheres (diameter 1-2 μm, shell thickness 100-200 nm) displayed excellent photocatalytic performance for overall water splitting under UV irradiation, affording H2 and O2 evolution rates of 240 and 116 μmol h-1 g-1 , respectively. Following decoration with 0.5 wt % Pt, the H4 Nb2 O7 hollow microspheres demonstrated remarkably high H2 and O2 evolution rates of 1240 and 600 μmol h-1 g-1 , respectively. To our knowledge, this work is the first reported study examining the photocatalytic performance of H4 Nb2 O7 for water splitting. The hydrothermal synthesis method described here is also applicable to the synthesis of pyrochlore H4 Ta2 O7 from Sn2 Ta2 O7 , highlighting the versatility of the approach.

Engineering Zn1–xCdxS/CdS Heterostructures with Enhanced Photocatalytic Activity

Various porous Zn1-xCdxS/CdS heteorostructures were achieved via in situ synthesis method with organic amines as the templates. Because of the larger radius of Cd(2+) than that of Zn(2+), CdS quantum dots are formed and distributed uniformly in the network of Zn1-xCdxS. The Zn1-xCdxS/CdS heterostructure with small Cd content (10 at%) derived from ethylenediamine shows very high H2-evolution rate of 667.5 μmol/h per 5 mg photocatalyst under visible light (λ ≥ 420 nm) with an apparent quantum efficiency of 50.1% per 5 mg at 420 nm. Moreover, this Zn1-xCdxS/CdS heterostructure photocatalyst also shows an excellent photocatalytic stability over 100 h.

Preparation of Ba3In2(OH)12 and its Photocatalytic Performance

Hydrogarnet Ba3In2(OH)12 was synthesized by hydrothermal method from raw materials Ba(NO3)2 and In(OH)3. The obtained sample was characterized by X-ray diffraction (XRD), scanning electron microscope(SEM), UV-visible diffuse reflectance spectroscopy (UV-vis DRS) and N2 adsorption-desorption isotherms (BET). Photocatalyitc activity was tested via rhodamine B(RhB) degradation as the modle pollutant. The influence of hydrothermal reaction temperature (T), hydrothermal reaction time (t), Ba/In molar ratio(Ba/In), and NaOH concentration(Cg) on the photocatalytic activity of Ba3In2(OH)12 were investigated. The results showed that the synthetic Ba3In2(OH)12 exhibited highest photocatalytic activity under the optimum hydrothermal reaction conditions of T=200°C, t=14 h, Ba/In=2:1 and Cg=7 mol/L. RhB can be completely mineralized by Ba3In2(OH)12 under 125 W mercury light irradiation for 3 hours. There are many scholars and experts engaged in the research of various types of photocatalytic materials and applied in the degradation of environmental pollutants in the last 40 years. Such as, the oxide of In2O3[1], ZnO, TiO2 et al. The ternary oxide of indium, molybdate, tungstate and vanadate et al. New type quaternary metal oxide. In the past 20 years, indium-based semiconductor material were got rapid development in the field of display, laser, microwave devices, light-emitting diodes and photocatalyst because of which had good gas sensitivity, heat sensitivity, photosensitivity and other characteristics. CaIn2O4 was synthesized using self-propagating high-temperature sysnthesis method[2]. RhB can be absolutely mineralized under solar irradiation for 2 hours. The g-C3N4/CaIn2O4 composite was synthesized using facile solvothermal method[3]. The g-C3N4/CaIn2O4 composite reached a high H2 evolution rate of 62.5 μmol/h from CH3OH/ H2O solution when the content of grapheme was 1wt%. Furthermore, the 1wt% g-C3N4/CaIn2O4 composite did not show deactivation for H2 evolution for longer than 32 h. The core-shell like composite In2O3@Ba2In2O5 was synthesized via chemical impregnation method with sample calcination[4]. It degraded 100% of the MB in 30 min compared with P-25, which degraded 100% of the MB in 120 min. C-CdIn2O4 nanoparticle was synthesized by sol-gel templating method[5]. Natural sunlight illumination experiments showed the H2 evolution rate of C-CdIn2O4 was 17 μmol/h as compared to 2.1 μmol/h for the Pt:TiO2. Hydrogarnet Ba3In2(OH)12 was first described by Kwestroo et al in 1977, who used the prolonged refluxing of BaCl2 and In2O3 in 12 mol/L NaOH at 110°C[6]. The pure Ba3In2(OH)12 was prepared by first preparing pure Ba3In2O6 by prolonged reaction of stoichiometric amounts of BaCO3 and In2O3 at 1300 °C. Then, the pure Ba3In2O6 was reacted with 12 mol/L NaOH at 85 °C for 12 hours under a pure nitrogen atmosphere[7]. Hydrogarnet Ba3In2(OH)12 was synthesized by hydrothermal method, using In(OH)3, Ba(NO3)2 and NaOH. With RhB as a model degradation pollutant, the influence of hydrothermal reaction temperature, hydrothermal reaction time, Ba/In molar ratio and NaOH concentration on the photocatalytic activity of Ba3In2(OH)12 were investigated and the photocatalytic degradation mechanism of RhB were investigated. The results can provide references for the research and application of this material system in the future.

Mo2C as Non‐Noble Metal Co‐Catalyst in Mo2C/CdS Composite for Enhanced Photocatalytic H2Evolution under Visible Light Irradiation

Co-catalysts are a major factor to enhance photocatalytic H2 activity; they are mainly composed of expensive noble metals. Here, we reported a new non-noble-metal co-catalyst Mo2 C that efficiently improves the photocatalytic H2 evolution of CdS under visible light irradiation. Mo2 C is prepared by temperature-programmed reaction with molybdenum oxide as precursor, and the Mo2 C/CdS composite is prepared by deposition of CdS on Mo2 C. The optimum composite 2.0 % Mo2 C/CdS shows a high H2 evolution rate of 161 μmol h(-1) , which is ten times higher than that of CdS alone and 2.3 times higher than the optimum for 1.0 % Pt/CdS. Moreover, the Mo2 C/CdS is stable for 50 h. This study presents a new low-cost non-noble-metal co-catalyst as a photocatalyst to achieve highly efficient H2 evolution.

Reduced Graphene Oxide-Ag3PO4 Heterostructure: A Direct Z-Scheme Photocatalyst for Augmented Photoreactivity and Stability.

A visible light driven, direct Z-scheme reduced graphene oxide-Ag3PO4 (RGO-Ag3 PO4 ) heterostructure was synthesized by means of a simple one-pot photoreduction route by varying the amount of RGO under visible light illumination. The reduction of graphene oxide (GO) and growth of Ag3PO4 took place simultaneously. The effect of the amount of RGO on the textural properties and photocatalytic activity of the heterostructure was investigated under visible light illumination. Furthermore, total organic carbon (TOC) analysis confirmed 97.1 % mineralization of organic dyes over RGO-Ag3PO4 in just five minutes under visible-light illumination. The use of different quenchers in the photomineralization suggested the presence of hydroxyl radicals ((.)OH), superoxide radicals ((.)O2 (-)), and holes (h(+)), which play a significant role in the mineralization of organic dyes. In addition to that, clean hydrogen fuel generation was also observed with excellent reusability. The 4 RGO-Ag3PO4 heterostructure has a high H2 evolution rate of 3690 μmol h(-1) g(-1), which is 6.15 times higher than that of RGO.

Photocatalytic hydrogen evolution by Cu(II) complexes.

[Cu(TMPA)Cl]Cl (1) and [Cu(Cl-TMPA)Cl2] (2) exhibited efficient photocatalytic H2 evolution with a TON of 6108 and 10014 (6 h), respectively, in CH3CN/H2O solution (9 : 1, v/v) containing an Ir complex as the photosensitizer and triethylamine as the sacrificial reductant, representing the first example of photocatalytic Cu complex-based water reduction catalysts.

A novel and highly efficient earth-abundant Cu3P with TiO2 "P-N" heterojunction nanophotocatalyst for hydrogen evolution from water.

Semiconductor-based photocatalytic hydrogen (H2) evolution from water is of great importance for solar-to-chemical conversion processes to boost and promote the future hydrogen economy. Here, for the first time, we demonstrate that p-Cu3P coupled with n-TiO2 forms a novel hybrid structure which accelerates electron-hole pair separation and transfer for improved photocatalytic H2-evolution activity. The rate of H2 evolution of the optimized Cu3P/TiO2 (7940 μmol h-1 g-1) is 11 times higher than that of bare TiO2, with an apparent quantum efficiency (AQE) of 4.6%. This work may provide more insight into the synthesis of novel phosphide-based hybrid materials with high photocatalytic H2-evolution activity and sufficient stability for solar-to-chemical conversion and utilization.

NiFeSe]-hydrogenase chemistry.

The development of technology for the inexpensive generation of the renewable energy vector H2 through water splitting is of immediate economic, ecological, and humanitarian interest. Recent interest in hydrogenases has been fueled by their exceptionally high catalytic rates for H2 production at a marginal overpotential, which is presently only matched by the nonscalable noble metal platinum. The mechanistic understanding of hydrogenase function guides the design of synthetic catalysts, and selection of a suitable hydrogenase enables direct applications in electro- and photocatalysis. [FeFe]-hydrogenases display excellent H2 evolution activity, but they are irreversibly damaged upon exposure to O2, which currently prevents their use in full water splitting systems. O2-tolerant [NiFe]-hydrogenases are known, but they are typically strongly biased toward H2 oxidation, while H2 production by [NiFe]-hydrogenases is often product (H2) inhibited. [NiFeSe]-hydrogenases are a subclass of [NiFe]-hydrogenases with a selenocysteine residue coordinated to the active site nickel center in place of a cysteine. They exhibit a combination of unique properties that are highly advantageous for applications in water splitting compared with other hydrogenases. They display a high H2 evolution rate with marginal inhibition by H2 and tolerance to O2. [NiFeSe]-hydrogenases are therefore one of the most active molecular H2 evolution catalysts applicable in water splitting. Herein, we summarize our recent progress in exploring the unique chemistry of [NiFeSe]-hydrogenases through biomimetic model chemistry and the chemistry with [NiFeSe]-hydrogenases in semiartificial photosynthetic systems. We gain perspective from the structural, spectroscopic, and electrochemical properties of the [NiFeSe]-hydrogenases and compare them with the chemistry of synthetic models of this hydrogenase active site. Our synthetic models give insight into the effects on the electronic properties and reactivity of the active site upon the introduction of selenium. We have utilized the exceptional properties of the [NiFeSe]-hydrogenase from Desulfomicrobium baculatum in a number of photocatalytic H2 production schemes, which are benchmark systems in terms of single site activity, tolerance toward O2, and in vitro water splitting with biological molecules. Each system comprises a light-harvesting component, which allows for light-driven electron transfer to the hydrogenase in order for it to catalyze H2 production. A system with [NiFeSe]-hydrogenase on a dye-sensitized TiO2 nanoparticle gives an enzyme-semiconductor hybrid for visible light-driven generation of H2 with an enzyme-based turnover frequency of 50 s(-1). A stable and inexpensive polymeric carbon nitride as a photosensitizer in combination with the [NiFeSe]-hydrogenase shows good activity for more than 2 days. Light-driven H2 evolution with the enzyme and an organic dye under high O2 levels demonstrates the excellent robustness and feasibility of water splitting with a hydrogenase-based scheme. This has led, most recently, to the development of a light-driven full water splitting system with a [NiFeSe]-hydrogenase wired to the water oxidation enzyme photosystem II in a photoelectrochemical cell. In contrast to the other systems, this photoelectrochemical system does not rely on a sacrificial electron donor and allowed us to establish the long sought after light-driven water splitting with an isolated hydrogenase.