Photocatalytic H2 production from water splitting under visible light irradiation using Eosin Y-sensitized mesoporous-assembled Pt/TiO2 nanocrystal photocatalyst

Sensitized photocatalytic production of hydrogen from water splitting is investigated under visible light irradiation over mesoporous-assembled titanium dioxide (TiO₂) nanocrystal photocatalysts, without and with Pt loading. The photocatalysts are synthesized by a sol–gel process with the aid of a structure-directing surfactant and are characterized by N₂ adsorption–desorption analysis, X-ray diffraction, UV–vis spectroscopy, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray analysis. The dependence of hydrogen production on the type of TiO₂ photocatalyst (synthesized mesoporous-assembled and commercial non-mesoporous-assembled TiO₂ without and with Pt loading), the calcination temperature of the synthesized photocatalyst, the sensitizer (Eosin Y) concentration, the electron donor (diethanolamine) concentration, the photocatalyst dosage and the initial solution pH is systematically studied. The results show that in the presence of the Eosin Y sensitizer, the Pt-loaded mesoporous-assembled TiO₂ synthesized by a single-step sol–gel process and calcined at 500 °C exhibits the highest photocatalytic activity for hydrogen production from a 30 vol.% diethanolamine aqueous solution with dissolved 2 mM Eosin Y. Moreover, the optimum photocatalyst dosage and initial solution pH for the maximum photocatalytic activity for hydrogen production are 3.33 g dm⁻³ and 11.5, respectively.     

Photocatalytic hydrogen production over CuO and TiO2 nanoparticles mixture

Cheap and efficient photocatalysts were fabricated by simply mixing TiO₂ nanoparticles (NPs) and CuO NPs. The two NPs combined with each other to form TiO₂/CuO mixture in an aqueous solution due to the opposite surface charge. The TiO₂/CuO mixture exhibited photocatalytic hydrogen production rate of up to 8.23 mmol h⁻¹ g⁻¹ under Xe lamp irradiation when the weight ratio of P25 to CuO was optimized to 10. Although the conduction band edge position of CuO NPs is more positive than normal hydrogen electrode, the TiO₂/CuO mixture exhibited good photocatalytic hydrogen production performance because of the inter-particle charge transfer between the two NPs. The detailed mechanism of the photocatalytic hydrogen production is discussed. This mixing method does not require a complicated chemical process and allows mass production of the photocatalysts.     

The use of products from CO2 photoreduction for improvement of hydrogen evolution in water splitting

CuO/TiO₂ photocatalysts were prepared and shown to enhance the rate of CO₂ photoreduction and the production of total organic carbon (TOC), including HCOOH, HCHO and CH₃OH. Resulting TOC could act as electron donors for enhancing visible light hydrogen evolution from Pt/TiO₂ photocatalysts. The impacts on CO₂ photoreduction were investigated including the effect of Cu dopant, pH, irradiation time and using Na₂SO₃ as a sacrificial agent, and those on hydrogen evolution was also studied including TOC concentration and Pt doping. The CO₂ photoreduction mechanisms with respect to pH and CO₂ reduction potentials were discussed. CuO/TiO₂ and Pt/TiO₂ photocatalysts were characterized by X-ray diffraction, Raman spectroscopy and diffuse reflection UV-vis spectrophotometry. Both photocatalysts showed a visible light response in comparison with pure TiO₂. The photocatalytic experiments and FT-IR spectra indicated that photoproduct desorption was the rate-limiting step in the CO₂ photoreduction.     

Electrospun Pt/TiO2 hybrid nanofibers for visible-light-driven H2 evolution

One-dimensional (1D) Pt/TiO₂ hybrid nanofibers (HNFs) with different concentrations of Pt were fabricated by a facile two-step synthesis route combining an electrospinning technique and calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) results showed that the Pt nanoparticles (NPs) with the size of 5–10 nm were well dispersed in the TiO₂ nanofibers (NFs). Further investigations from the UV–Vis diffuse reflectance (DR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that some Pt ions were incorporated into the TiO₂ lattice as Pt⁴⁺ state, which contributed to the visible light absorption of TiO₂ NFs. Meanwhile, the Pt²⁺ ions existing on the surface of Pt NPs resulted in the formation of Pt–O–Ti bond at Pt NPs/TiO₂ NFs interfaces that might serve as an effective channel for improving the charge transfer. The as-electrospun Pt/TiO₂ HNFs exhibited remarkable activities for photocatalytic H₂ evolution under visible light irradiation in the presence of l-ascorbic acid as the sacrificial agent. In particular, the optimal HNFs containing 1.0 at% Pt showed the H₂ evolution rate of 2.91 μmol h⁻¹ and apparent quantum efficiency of 0.04% at 420 nm by using only 5 mg of photocatalysts. The higher photocatalytic activity could be ascribed to the appropriate amount of Pt ions doping and excellent electron-sink effect of Pt NPs co-catalysts.     

CoNi bimetallic alloy cocatalyst-modified TiO2 nanoflowers with enhanced photocatalytic hydrogen evolution

In terms of improving photocatalytic hydrogen production performance, inexpensive and earth-rich cocatalysts have become promising alternatives to precious metals. Herein, a novel CoNi–TiO₂ photocatalyst composed of TiO₂ nanoflowers and CoNi alloy was prepared by hydrothermal and chemical reduction methods. Various characterizations and test results have confirmed that the further improvement of the photocatalytic performance of the CoNi–TiO₂ photocatalyst is mainly due to the fact that the bimetallic CoNi alloy can accelerate charge transfer and inhibit the recombination of photo-induced carriers. The hydrogen production rate of the prepared CoNi–TiO₂ is about 24 times higher than that of the pristine TiO₂, and its hydrogen production rate value can reach 6580.9 μmol g^?1 h^?1, and showing comparable photocatalytic performance to 0.5 wt% Pt–TiO₂. In addition, combined with the characterization results, a probable mechanism for enhanced photocatalytic performance was proposed. This study provides favorable enlightenment for the design of a series of highly efficient non-precious metal TiO₂-based photocatalysts.     

Light-assisted synthesis of Au/TiO2 nanoparticles for H2 production by photocatalytic water splitting

A series of Au/TiO₂ photocatalysts was synthesized via the light assistance through the photo-deposition for H₂ production by photocatalytic water splitting using ethanol as the hole scavenger. Effect of solution pH in the range of 3.2–10.0 on the morphology and photocatalytic activity for H₂ production of the obtained Au/TiO₂ photocatalysts was explored. It was found that all Au/TiO₂ photocatalysts prepared in different solution pH exhibited comparable anatase fraction (～0.84–0.85) and crystallite size of TiO₂ (21–22 nm), but showed different quantity of deposited Au nanoparticles (NPs) and other properties, particularly the particle size of the Au NPs. Among all prepared Au/TiO₂ photocatalysts, the Au/TiO₂ (10.0) photocatalyst exhibited the highest photocatalytic activity for H₂ production, owning to its high metallic state and small size of Au NPs. Via this photocatalyst, the maximum H₂ production of 296 μmol (～360 μmol/g?h) was gained at 240 min using the 30 vol% ethanol as the hole scavenger at the photocatalyst loading of 1.33 g/L under the UV light intensity of 0.24 mW/cm² with the quantum efficiency of 61.2% at 254 nm. The loss of the photocatalytic activity of around 20% was observed after the 5th use.     

Effects of the preparation order of the ternary P25/GO/Pt hybrid photocatalysts on hydrogen production

In this study, ternary P25/GO/Pt hybrid photocatalysts are prepared in different orders, using Degussa's TiO₂ (P25), graphene oxide (GO), chloroplatinic acid as precursor. The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). This work is first time to compare the hydrogen production of the ternary P25/GO/Pt hybrid photocatalysts prepared in different orders. We focus on studying the introduction of GO and find that the quantity of introduced GO and electronic transfer path play an important role in photocatalytic activity on ternary P25/GO/Pt hybrid catalysts. When the proper Pt particle loaded on the flat surface of GO which was 0.5wt% of P25, the highest H₂ evolution was obtained.     

Hydrogen production using Pt-loaded TiO2 photocatalysts

A series of synthesised TiO₂-based and commercial photocatalysts were modified by Pt photodeposition and a study made of their photocatalytic activity in hydrogen production. The modified commercial photocatalysts were Evonik P25, Kronos vlp7000 and Hombikat UV-100, and the other modified photocatalysts were synthesised by our group using sol–gel and sol–gel hydrothermal processes (SG400, SG750 and HT). Pt weight percentages used in the study were 0.5, 1.0 and 2.1 wt.% (Pt/TiO₂). The photocatalysts were extensively characterised by X-ray diffraction (XRD), UV–vis diffuse reflectance, Brunauer–Emmett–Teller (BET) surface area measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM–EDX), Fourier transform infrared spectroscopy (FTIR) and laser light dispersion. Methanol (25% vol.) was used as sacrificial agent over the 8 h of the hydrogen production tests and measurements were taken of the final concentrations of formaldehyde and formic acid as well as initial and final TOC. Photoactivity of all photocatalysts increased in the presence of Pt. The most efficient of the synthesised photocatalysts was SG750 and of the commercial photocatalysts P25. Maximum production of SG750 was 1846 μmol h⁻¹ at 1.0 wt.% Pt and its production per surface unit was notably higher than that of P25.     

Photocatalytic properties of redox-treated Pt/TiO2 photocatalysts for H2 production from an aqueous methanol solution

The influence of redox-treated Pt/TiO₂ photocatalysts on H₂ production is investigated. Catalyst characterizations are performed by TEM, XPS, XRD, BET, and UV–vis/DR spectroscopy techniques. In terms of production rate, the oxidation treatment shows higher reactivity than the reduction treatment. The reduction treatment allows the formation of metallic Pt(0), which more easily catalyzes the transition of TiO₂ from the anatase to the rutile phases. Reduction-treated Pt/TiO₂ photocatalysts have lower S_BET values than oxidation-treated Pt/TiO₂ photocatalysts due to the higher percentage of TiO₂ in the rutile phase. Combining the results of XPS and optical analyses, PtO/TiO₂ shows a higher energy band gap than metallic Pt(0)/TiO₂, indicating that oxidation-treated Pt/TiO₂ is more capable of achieving water splitting for H₂ production. According to the results of this study, the oxidation treatment of Pt/TiO₂ photocatalysts can significantly enhance the reactivity of photocatalytic H₂ production because of their homogenous distribution, lower phase transition, higher S_BET, and higher energy band gap.     

Photo-induced reforming of alcohols with improved hydrogen apparent quantum yield on TiO2 nanotubes loaded with ultra-small Pt nanoparticles

Photo-induced reforming of methanol, ethanol, glycerol and phenol at room temperature for hydrogen production was investigated with the use of ultra-small Pt nanoparticles (NPs) loaded on TiO₂ nanotubes (NTs). The Pt NPs with diameters between 1.1 and 1.3 nm were deposited on TiO₂ NTs by DC-magnetron sputtering (DC-MS) technique. The photocatalytic hydrogen rate achieved an optimum value for a loading of about 1 wt% of Pt. Apparent quantum yield for hydrogen generation was measured for methanol and ethanol water solutions reaching a maximum of 16% under irradiation with a wavelength of 313 nm in methanol/water solution (1/8 v/v). Pt NPs loaded on TiO₂ NTs represented also a true water splitting catalyst under UV irradiation and pure distilled water. DC-MS method appears to be a technologically simple, ecologically benign and potentially low-cost process for production of an efficient photocatalyst loaded with ultra-small NPs with precise size control.     

Photocatalytic H2 generation from ethanol and glucose aqueous solutions by PtOx/TiO2 composites

A new straightforward protocol for the deposition of the platinum oxide (PtO–PtO₂) particles onto the TiO₂ semiconductor via controllable hydrolysis of the sulfuric acid solution of Pt(IV) hydroxide was developed. The developed approach represents a simple and “green” way to prepare the supported Adams-type catalysts. In the constructed composites (PtO₂·xH₂O/TiO₂) the Pt ionic species (hydrated PtO and PtO₂ nanoparticles) weakly interact with the titania surface, but under heating the Pt–O–Ti bonds are established, resulting in the stabilization of the Pt(II) ionic state. This state dominates in the obtained catalysts PtO_x/TiO₂ with a low platinum loading, while at a higher Pt content the metallic Pt particles also appear. The prepared PtO_x/TiO₂ photocatalysts have been successfully tested in the production of hydrogen under UV light from aqueous solutions of ethanol and glucose, the products of starch biomass processing. Appreciable activity in the production of hydrogen from water/ethanol mixtures was achieved, even at a Pt content of up to 0.05%. PtO_x/TiO₂ photocatalysts with Pt content of 0.2–0.4 wt% have been successfully used to produce hydrogen from aqueous glucose solutions, and PtO_x(0.29)/TiO₂ photocatalyst has demonstrated an exceptionally high rate of H₂ production per gram of platinum introduced and the quantum efficiency comparable to the highest published values.     

Enhanced hydrogen generation from methanol aqueous solutions over Pt/MoO3/TiO2 under ultraviolet light

The photocatalytic activity in hydrogen production from methanol reforming can be significantly enhanced by Pt/MoO₃/TiO₂ photocatalysts. Compared with Pt/P25, the photocatalytic activity of optimized Pt/MoO₃/TiO₂ shows an evolution rate of 169 μmol/h/g of hydrogen, which is almost two times higher than that of Pt/P25. XRD and Raman spectra show that MoO₃ are formed on the surface of TiO₂. It is found that with the bulk MoO₃ just formed, the catalyst shows the highest activity due to a large amount of heterojunctions and the high crystallinity of MoO₃. The HRTEM image showed a close contact between MoO₃ and TiO₂. It is proposed that the Z-scheme type of heterojunction between MoO₃ and TiO₂ is responsible for the improved photocatalytic activity. The heterojunction structure of MoO₃/TiO₂ does not only promote the charge separation, but also separates the reaction sites, where the oxidation (mainly on MoO₃) and reduction (on TiO₂) reactions occurred.     

Photodeposited-metal/CdS/ZnO heterostructures for solar photocatalytic hydrogen production under different conditions

In this study, photocatalytic hydrogen production over metal-incorporated CdS and ZnO (M/CdS/ZnO) nanocomposites under simulated solar light illumination was investigated. M/CdS/ZnO samples were synthesized by photodepositing a metal into CdS/ZnO powders. All photocatalysts showed increased hydrogen production with an increase in the light exposure time. The M/CdS/ZnO samples exhibited better hydrogen production yields than the CdS/ZnO nanocomposites, which in turn showed higher hydrogen production yields than pure ZnO did. The hydrogen production yields of the CdS/ZnO samples increased as the CdS/ZnO weight ratio increased from 0.01 to 0.10. However, they decreased with further increases in CdS loading, although the light absorption edges of the CdS/ZnO samples were further extended to the visible region. Pt/CdS/ZnO and Pd/CdS/ZnO exhibited similar hydrogen production yields, which were higher than the Ni/CdS/ZnO yield. The hydrogen production yield of Pt (0.5%)/CdS/ZnO was higher than that of Pt (0.1%)/CdS/ZnO. Notably, the hydrogen production yield of CdS/Pt/ZnO was lower than that of Pt/CdS/ZnO. Among three different electron donors (Na₂S + Na₂SO₃, methanol, and lactic acid solutions), the Na₂S + Na₂SO₃ solution led to the highest hydrogen production yield. A tentative mechanism for photocatalytic hydrogen production over M/CdS/ZnO nanocomposites under solar light irradiation, using a Na₂S + Na₂SO₃ solution as an electron donor, was proposed. In summary, M/CdS/ZnO photocatalysts can be utilized efficiently for photocatalytic hydrogen production with solar light exposure through proper control of operating parameters.     

Photocatalytic production of hydrogen and methane from glycerol reforming over Pt/TiO2–Nb2O5

In this study, platinized mixed oxides (TiO₂–Nb₂O₅) were tested on photocatalytic hydrogen production from a glycerol solution under UV light. Different samples with different Ti:Nb ratios were prepared by using a simple method that simultaneously combined a physical mixture and a platinum photochemical reduction. This method led to improved physicochemical properties such as low band gap, better Pt nanoparticle distribution on the surface, and the formation of different Pt species. Niobia content was also found to be an important factor in determining the overall efficiency of the Pt–TiO₂–Nb₂O₅ photocatalyst in the glycerol reforming reaction. The photocatalytic results showed that Pt on TiO₂–Nb₂O₅ enhanced hydrogen production from the aqueous glycerol solution at a 5 wt% initial glycerol concentration. The influence of different operating conditions such as the catalyst dosage and initial glycerol concentration was also evaluated. The results indicated that the best hydrogen and methane production was equal to 6657 μmol/L and 194 μmol/L, respectively after 4 h of UV radiation using Pt/Ti:Nb (1:2) sample and with 3 g/L of catalyst dosage. Moreover, the role of water in photocatalytic hydrogen production was studied through photocatalytic activity tests in the presence of D₂O. The obtained results confirmed the role of water molecules on the photocatalytic production of hydrogen in an aqueous glycerol solution.     

Precursor self-derived Cu@TiO2 hybrid Schottky junction for enhanced solar-to-hydrogen evolution

Solar-to-hydrogen production has attracted increasing attention since it possesses great potential in alleviating energy and environmental crises to some extent. The key issue is to develop efficient photocatalysts exhibiting superior hydrogen production capability. In this work, Cu@TiO₂ hybrid (Cu nanoparticles encapsulated in TiO₂) has been successfully prepared by Cu₂O self-template reduction through solvothermal treatment in ethylene glycol-water mixed solvent. When octahedral Cu₂O is involved in the reaction system, the Cu₂O@Ti-precursor octahedral structure is first formed and subsequently the Cu@TiO₂ hybrid is prepared with the reduction of ethylene glycol (EG). The Cu@TiO₂ hybrid derived with different mass of Cu exhibits improved photocatalytic hydrogen production performance compare to pure TiO₂ and P25. Among those photocatalysts, the Cu@TiO₂-10% (the copper content is 10 wt%) shows the highest hydrogen evolution rate of 4336.7 μmol g^?1 h^?1, and it is twice as much as the pure TiO₂ and 1.9 times as much as P25, respectively. Based on the photo/electrochemical results, an efficient photo-generated electron-hole separation contributes to the enhancement of photocatalytic H₂ evolution upon the Cu@TiO₂ hybrid. When replacing octahedral Cu₂O with cubic and truncated octahedrons ones, the Cu@TiO₂ hybrid photocatalysts are also obtained and they also display superior solar-to-hydrogen evolution than pure TiO₂ and P25. It is expected this work could develop an approach to design Cu-encapsulated hybrid photocatalysts for hydrogen generation.     

Oxygen vacancy induced Pt-decorated MOF photocatalyst for hydrogen production

The photocatalytic performance has remained challenging due to the rapid recombination of photoexcited electron-hole (e-h) pairs. To overcome this problem, creating oxygen vacancies on the surface of semiconductors has been an effective strategy. Herein, we report the effects of oxygen vacancies (Ov) on photocatalytic HER performance of Pt nanoparticles (NPs) anchored on UiO-66-NH₂. In contrast, under the same amount of Pt NPs, UiO-66-NH₂ with high oxygen vacancies (denoted as Pt/UN-Ovh) exhibit superior photocatalytic H₂ generation than the catalyst with low oxygen vacancies (denoted as Pt/UN-Ovl) under visible-light irradiation. Based on the experimental characterization and theoretical calculations, the high oxygen vacancies not only stabilize the Pt NPs on the substrate (UiO-66-NH₂), but also develop the strong interaction between Pt NPs and support thereby Pt NPs traps more electrons from substrate and provides protons for H₂ production inhibiting the electron-hole recombination. This work provides novel strategy for enhancing the photocatalysts performance of MOF based materials.     

Photocatalytic H2 production from ethanol aqueous solution using TiO2 with tungsten carbide nanoparticles as co-catalyst

The effect of tungsten carbide as co-catalyst in the photocatalytic H₂ production from ethanol aqueous solutions (25% v/v) is reported. The photocatalytic H₂ production using WC/TiO₂ systems, in which tungsten carbide NPs are dispersed onto TiO₂, is compared with that of TiO₂800 with morphological and structural characteristics similar to WC/TiO₂ and with the hydrogen produced using commercial TiO₂ P25 as reference. To this end, W_xC_y/TiO₂, WC_1-x/TiO₂_US and WO₃/TiO₂ photocatalysts were prepared, characterized and tested. The preparation of W_xC_y/TiO₂ was accomplished by using a sol-gel based method which was useful for preparing bulk tungsten carbides. The preparation of WC_1-x/TiO₂_US is reported by the first time using a sonication method from WC_1-x and TiO₂800. Materials were characterized using N₂ physisorption, XRD, SEM-EDX, TEM-HRTEM, UV–vis RDS, XP and Raman spectroscopy. The presence of 2–3 nm NPs with different tungsten carbide crystalline phases (hexagonal WC and W₂C and cubic WC_1-x) was determined for W_xC_v/TiO₂ photocatalyst, the solely presence of 2–5 nm cubic WC_1-x NPs onto TiO₂ was confirmed for WC_1-x/TiO₂_US.The presence of tungsten carbide NPs onto TiO₂ improves the photocatalytic behavior of TiO₂ in terms of hydrogen production. The effect of tungsten carbide NPs in the C2–C4 products derived from ethanol is discussed and the reusability of the photocatalyst is also studied.     

The size and valence state effect of Pt on photocatalytic H2 evolution over platinized TiO2 photocatalyst

Photocatalytic hydrogen production from water or organic compounds is a promising way to resolve our energy crisis and environmental problems in the near future. Over the past decades, many photocatalysts have been developed for solar water splitting. However, most of these photocatalysts require cocatalyst to facilitate H₂ evolution reaction and noble metals as key cocatalysts are widely used. Consequently, the condition of noble metal cocatalyst including the size and valence state etc plays the key role in such photocatalytic system. Here, the size and valence state effect of Pt on photocatalytic H₂ evolution over platinized TiO₂ photocatalyst were studied for the first time. Surprisingly, it was found that Pt particle size does not affect the photoreaction rate with the size range of several nanometers in this work, while it is mainly depended on the valence state of Pt particles. Typically, TOFs of TiO₂ photodeposited with 0.1–0.2 wt% Pt can exceed 3000 h⁻¹.     

Effect of liquid phase plasma on photocatalysis of water for hydrogen evolution

This study examined the effects of liquid phase plasma irradiation on the photocatalytic decomposition of water for hydrogen evolution. TiO₂ and metal-loaded TiO₂ nanocrystallites were introduced as photocatalysts. Na-Y zeolite was applied as a support for the TiO₂ nanocrystallites. The photocatalytic activities of the photocatalysts were estimated for hydrogen production from water. Hydrogen evolution appeared in the photodecomposition of water without photocatalysts. This was caused by the decomposition of water by plasma irradiation in water directly. The hydrogen evolution efficiency improved with increasing conductivity of water. The rate of hydrogen evolution was increased by the metal loading (Ni, Co, Fe) on the TiO₂ surface. Na-Y zeolite can be used as an efficient photocatalytic support for the fixation of TiO₂. The TiO₂ nanocrystallites were incorporated above 40 wt% on Na-Y support.     

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

CuO_1?x cluster-modified TiO₂ (CuO_1?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 CuO_1?x/TiO₂ catalyst with only 1 wt% CuO_1?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 CuO_1?x nano clusters on the surface of the TiO₂. In addition, Pt/CuO_1?x/TiO₂ was also prepared by loading Pt on CuO_1?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 CuO_1?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.