High efficient electrocatalytic oxidation of methanol on Pt/polyindoles composite catalysts

Novel composite catalysts have been fabricated by the electrodeposition of Pt onto the glassy carbon electrode (GC) modified respectively with polyindole (PIn) and poly(5-methoxyindole) (PMI) and used for the electrooxidation of methanol in acid solution of 0.5 M H₂SO₄ containing 1.0 M methanol. As-formed composite catalysts are characterized by SEM, XRD and the electrochemical methods. The results of the catalytic activity for methanol oxidation show that the two composite catalysts exhibit higher catalytic activity and stronger poisoning-tolerance than Pt/polypyrrole/GC (Pt/PPy/GC) and Pt/GC. Electrochemical impedance spectroscopy indicates that the methanol electrooxidation on the composite catalysts at various potentials shows different impedance behaviors. At the same time, the charge-transfer resistance for electrooxidation of methanol on Pt/PIn/GC and Pt/PMI/GC is smaller than those on Pt/PPy/GC and Pt/GC. The present study shows a promising choice of Pt/PIn and Pt/PMI as composite catalysts for methanol electrooxidation.     

Electrochemical impedance studies on carbon supported PtRuNi and PtRu anode catalysts in acid medium for direct methanol fuel cell

The anodic Pt–Ru–Ni/C and the Pt–Ru/C catalysts for potential application in direct methanol fuel cell (DMFC) were prepared by chemical reduction method. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were carried out by using a glassy carbon working electrode covered with the catalyst powder in a solution of 0.5 mol L⁻¹ CH₃OH and 0.5 mol L⁻¹ H₂SO₄ at 25 °C. EIS information discloses that the methanol electrooxidation on the Pt–Ru–Ni/C catalyst at various potentials shows different impedance behaviors. The mechanism and the rate-determining step of methanol electrooxidation are changed with increasing potential. Its rate-determining steps are the methanol dehydrogenation and the oxidation reaction of adsorbed intermediate CO_ads and OH_ads in low (400–500 mV) and high (600–800 mV) potentials, respectively. The catalytic activity of the Pt–Ru–Ni/C catalyst is higher for methanol electrooxidation than that of the Pt–Ru/C catalyst. Its tolerance performance to CO formed as one of the intermediates of methanol dehydrogenation is also better than that of the Pt–Ru/C catalyst.     

Influence of metal oxide on LiBH4/2LiNH2/MgH2 system for hydrogen storage properties

In this study, various nanoscale metal oxide catalysts, such as CeO₂, TiO₂, Fe₂O₃, Co₃O₄, and SiO₂, were added to the LiBH₄/2LiNH₂/MgH₂ system by using high-energy ball milling. Temperature programmed desorption and MS results showed that the Li–Mg–B–N–H/oxide mixtures were able to dehydrogenate at much lower temperatures. The order of the catalytic effect of the studied oxides was Fe₂O₃ > Co₃O₄ > CeO₂ > TiO₂ > SiO₂. The onset dehydrogenation temperature was below 70 °C for the samples doped with Fe₂O₃ and Co₃O₄ with 10 wt.%. More than 5.4 wt.% hydrogen was released at 140 °C. X-ray diffraction indicated that the addition of metal oxides inhibited the formation of Mg(NH₂)₂ during ball milling processes. It is thought that the changing of the ball milling products results from the interaction of oxide ions in metal oxide catalysts with hydrogen atoms in MgH₂. The catalytic effect depends on the activation capability of oxygen species in metal oxides on hydrogen atoms in hydrides.     

Pt support of multidimensional active sites and radial channels formed by SnO2 flower-like crystals for methanol and ethanol oxidation

SnO₂ nanoflowers and nanorods have been synthesized by the hydrothermal method without using any capping agent. Both types of SnO₂ nanostructures are selected as a support of Pt catalyst for methanol and ethanol electrooxidation. The synthesized SnO₂ nanostructures and SnO₂ supported platinum (Pt/SnO₂) catalysts are characterized by X-ray diffraction, scanning electron microscope and high resolution transmission electron microscope. The electrocatalytic properties of the Pt/SnO₂ and Pt/C catalysts for methanol and ethanol oxidation have been investigated systematically by typical electrochemical methods. The influence of SnO₂ morphology on its electrocatalytic activity is comparatively investigated. The Pt/SnO₂ flower-shaped catalyst shows higher electrocatalytic activity and better long-term cycle stability compared with other electrocatalysts owing to the multidimensional active sites and radial channels of liquid diffusion.     

Platinum nanoparticles embedded in layer-by-layer films from SnO2/polyallylamine for ethanol electrooxidation

Self-assembled films from SnO₂ and polyallylamine (PAH) were deposited on gold via ionic attraction by the layer-by-layer (LbL) method. The modified electrodes were immersed into a H₂PtCl₆ solution, a current of 100 μA was applied, and different electrodeposition times were used. The SnO₂/PAH layers served as templates to yield metallic platinum with different particle sizes. The scanning tunnel microscopy images show that the particle size increases as a function of electrodeposition time. The potentiodynamic profile of the electrodes changes as a function of the electrodeposition time in 0.5 mol L⁻¹ H₂SO₄, at a sweeping rate of 50 mV s⁻¹. Oxygen-like species are formed at less positive potentials for the Pt–SnO₂/PAH film in the case of the smallest platinum particles. Electrochemical impedance spectroscopy measurements in acid medium at 0.7 V show that the charge transfer resistance normalized by the exposed platinum area is 750 times greater for platinum electrode (300 kΩ cm²) compared with the Pt–SnO₂/PAH film with 1 min of electrodeposition (0.4 kΩ cm²). According to the Langmuir–Hinshelwood bifunctional mechanism, the high degree of coverage with oxygen-like species on the platinum nanoparticles is responsible for the electrocatalytic activity of the Pt–SnO₂/PAH concerning ethanol electrooxidation. With these features, this Pt–SnO₂/PAH film may be grown on a proton exchange membrane (PEM) in direct ethanol fuel cells (DEFC).     

Design and preparation of highly active carbon nanotube-supported sulfated TiO2 and platinum catalysts for methanol electrooxidation

A novel electrocatalyst structure of carbon nanotube-supported sulfated TiO₂ and Pt (Pt-S-TiO₂/CNT) is reported. The Pt-S-TiO₂/CNT catalysts are prepared by a combination of improved sol-gel and ethylene glycol reduction methods. Transmission electron microscopy and X-ray diffraction show that the sulfated TiO₂ is amorphous and is coated uniformly on the surface of the CNTs. Pt nanoparticles of about 3.6 nm in size are homogenously dispersed on the sulfated TiO₂ surface. Fourier transform infrared spectroscopy analysis proves that the CNT surfaces are modified with sulfated TiO₂ and a high concentration of SO_x, and adsorbed OH species exist on the surface of the sulfated TiO₂. Electrochemical studies are carried out using chronoamperometry, cyclic voltammetry, CO stripping voltammetry and impedance spectroscopy. The results indicate that Pt-S-TiO₂/CNT catalysts have much higher catalytic activity and CO tolerance for methanol electrooxidation than Pt/TiO₂/CNTs, Pt/CNTs and commercial Pt/C.     

A facile method to synthesize well-dispersed PtRuMoOx and PtRuWOx nanoparticles and their electrocatalytic activities for methanol oxidation

PtRuMoO_x and PtRuWO_x catalysts supported on multi-wall carbon nanotubes (MWCNTs) are prepared by ultrasonic-assisted chemical reduction method. XRD measurements indicate that Pt exists as face-centered cubic structure, Ru is alloyed with platinum, and the metal oxides exist as an amorphous structure. TEM pictures show that PtRuMoO_x and PtRuWO_x catalysts are well dispersed on the surface of MWCNTs with the particle size of about 3 nm and a narrow particle size distribution. The electrochemical properties of the catalysts for methanol electrooxidation are studied by cyclic voltammetry (CV), chronoamperometry (CA) and chronopotentiometry (CP). The onset potentials for methanol oxidation on PtRuMoO_x and PtRuWO_x are more negative than that of pure Pt catalyst, shifting negatively by about 0.20 V and have better electrocatalytic activities than PtRu/MWCNTs.     

Synthesis,characterization and performance of a novel Ni–Co/GO-TiO2 for electrooxidation of methanol and ethanol

In order to find out electrocatalysts based on non-precious metals, Ni–Co/GO-TiO₂ composite with different amounts of nickel and cobalt is prepared and the impacts of TiO₂ nanoparticles on GO support are highlighted. Composition, morphology and textural features of the synthesized materials are characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, N₂ adsorption-desorption isotherms and field emission scanning electron microscopy equipped with energy-dispersive X-ray analysis. The electrochemical activity of the prepared catalysts toward methanol and ethanol electrooxidation in alkaline media is investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. Results confirmed that adding TiO₂ nanoparticles to graphene oxide can increase the surface area, porosity and electrochemically active surface area of the support material. The composition with the equal amount of nickel and cobalt precursors exhibited the highest current density for methanol and ethanol electrooxiation equal to 121.07 and 145.28 mA/cm², respectively. Stability test results demonstrated that this sample maintains 94.1% and 87.5% of initial current density after 7200 s for the electrooxidation of ethanol and methanol in 1.0 M KOH, respectively. All results confirm the synergic effect of Ni and Co for the alcohols oxidation in alkaline media and equal amount of Ni and Co leads to the best catalytic performance with the highest current density, lowest impedance and maximum stability.     

Cycle durability of metal oxide supports for PEFC electrocatalysts

In order to develop durable electrocatalysts for polymer electrolyte fuel cells, six different metal oxides, namely MoO₃, SnO₂, Nb₂O₅, Ta₂O₅, TiO₂, and WO₃, are selected as thermochemically stable, carbon-free platinum electrocatalyst support materials. The stability of Pt on these alternative oxide support materials is systematically analyzed, for the first time, using common experimental protocols simulating realistic fuel cell vehicle operation. Pt/SnO₂ shows the best performance in terms of both electrochemical activity, and stability against dissolution. Pt dissolution rates in Pt/SnO₂ are comparable to those of conventional Pt/C electrocatalysts. These results suggest that SnO₂ is a promising candidate as an alternative electrocatalyst support.     

Abundant hydrogen production over well dispersed nickel nanoparticles confined in mesoporous metal oxides in partial oxidation of methane

To improve the stability of Ni catalysts and employ reactive oxygen species in reducible metal oxides, the Ni nanoparticles were confined within mesoporous metal oxides (La₂O₃, Yb₂O₃, ZrO₂, CeO₂) via evaporation-induced self assembly technique utilizing 3D honeycomb-like silica as substrate for partial oxidation of methane (POM). Compared with supported catalysts, the prepared catalysts showed superior catalysts stability especially 3D honeycomb-like ZrO₂ and CeO₂ supported Ni catalysts (Ni/3HL-ZrO₂-SiO₂ and Ni/3HL-CeO₂-SiO₂) due to confinement effect and strong interaction between Ni and metal oxides. CH₄ conversion reached 90%–92%. Outstanding catalytic activity was attributed to highly dispersity of active metal. More importantly, abundant hydrogen production was observed over mesoporous CeO₂, ZrO₂ supported catalysts and the ratio of H₂/CO changed from nominal value 2 to 3. DFT theoretical calculations illuminated structural defect sites of reducible support like CeO₂, ZrO₂ afforded generation of surface hydroxyl group, which can be regenerated by activation of water and reoxidation of CeO₂, ZrO₂. Hydroxyl group was beneficial to accelerate greatly water gas shift reaction, promoting the production of hydrogen. This may provide a strategy to regulate production composition of POM to expand its downstream process.     

Highly dispersed phase of SnO2 on TiO2 nanoparticles synthesized by polyol-mediated route: Photocatalytic activity for hydrogen generation

TiO₂–SnO₂ mixed oxides (Ti:Sn = 98:2 (TS2), 95:5 (TS5) and 90:10 (TS10) by atomic weight) of large surface area and small particle size, in which SnO₂ is in a dispersed phase on TiO₂, have been synthesized by a polyol-mediated route. Characterization by various techniques has shown that a highly dispersed phase of SnO₂ on anatase TiO₂ is formed in TS2 sample. No separate discernible phases corresponding to cassiterite SnO₂ or rutile TiO₂ is seen in TS2 sample, whereas rutile TiO₂ and SnO₂ are observed besides the anatase phase of TiO₂ in TS5 and TS10 samples. The average particle size of the mixed oxide samples is ～20 nm. All samples absorb visible light and the onset of absorption was ～425 nm. These mixed oxides show emission from defect levels arising due to the anion vacancies present in TiO₂. The visible light absorption of these samples is attributed to the presence of defect levels in the bandgap of TiO₂. Photocatalytic activity of these samples for hydrogen generation from water using methanol as sacrificial reagent was studied under sunlight type radiation. The results indicate that mixed oxides have better activity compared to pure TiO₂ synthesized by the same method and the activity decreases with increasing SnO₂ concentration in TiO₂. The enhanced activity of TS2 sample is ascribed to the efficient charge separation from TiO₂ to SnO₂ owing to the high dispersion of SnO₂ in TiO₂. The decreased photocatalytic activity with increased SnO₂ concentration is due to the aggregation of SnO₂ on TiO₂, which results in relatively poor dispersion of SnO₂ and decreased charge transfer efficiency, but still maintains better photocatalytic activity compared to TiO₂. In addition loading Pd co-catalyst produces a pronounced increase in the hydrogen yield due to the accumulation of electrons in the metal from the TiO₂ and SnO₂ semiconductors and the increased reductive power of the Pd loaded mixed oxide nanoparticles.     

Investigation of the nanometals (Ni and Sn) in platinum binary and ternary electrocatalysts for methanol electrooxidation

The main purpose of our research is focused to increase anodic catalysts activity and thus to decrease noble metal loading in anodes for electrooxidation of methanol. Binary and ternary catalysts dispersed in chitosan, Pt-Ni, Pt-Sn and Pt-Ni-Sn are synthesized by reduction of appropriate metal salts with NaBH₄ in the chitosan solution. UV-vis spectra and transmission electron microscopy (TEM) images of the catalysts reveal the presence of metal nanoparticles (NPs). Performance of Pt-Ni, Pt-Sn, and Pt-Ni-Sn nanocomposites for methanol electrooxidation are examined by cyclic voltammetery and chronoamperometry methods. The effect of some experimental factors such as methanol, chitosan and electrolyte (H₂SO₄) concentrations, Ni and Sn amounts dispersed in chitosan on the current density and potential for the oxidation of methanol are studied and optimized. The electrochemical measurements show that the activity of Pt-Ni-SnNPs catalyst for methanol electrooxidation is higher than the activity of PtNPs, Pt-NiNPs and Pt-SnNPs catalysts.     

The effect of Sn on platinum dispersion in Pt/graphene catalysts for the methanol oxidation reaction

Sn-modified platinum catalysts are presently one of the most active catalysts for the room temperature electrooxidation of ethanol at low potentials. In this study, Pt–Sn/graphene catalysts containing different ratios of Pt and Sn were prepared by the solution-phase reduction. Microstructural characterization shows that metallic Pt, Pt–Sn alloy and tin dioxide (SnO₂) nanoparticles are distributed on the graphene sheets in the synthetic process. In terms of the electrocatalytic properties, graphene-supported Pt–Sn catalysts exhibit much higher current densities with increasing Sn proportions. It's proved that the addition of Sn not only decreases catalyst particles growth and agglomeration, but also promotes methanol electrooxidation by geometric effects on expanding Pt's lattice spacing, causing a synergistic effect between Pt and Sn nanoparticles.     

Water-gas shift of reformate streams over mono-metallic PGM catalysts

Mono-metallic Pt and Rh catalysts supported on both CeO₂ and TiO₂ were prepared and tested for water-gas shift activity in a Flowrence, high throughput reactor system. The feed composition mimicked a typical fuel processor, steam methane reformer outlet stream. The Pt/CeO₂ catalyst showed the best metal activity of ～3.8 E-07 moles CO converted·gPt^-1 s^-1, at a Pt loading of 0.5 wt%, activity decreasing with increasing metal loading. Furthermore, the Pt/CeO₂ catalyst produced almost no methane while the Rh based catalysts led to substantial methanation.     

Study of poly(vinyl alcohol)/titanium oxide composite polymer membranes and their application on alkaline direct alcohol fuel cell

The novel poly(vinyl alcohol)/titanium oxide (PVA/TiO₂) composite polymer membrane was prepared using a solution casting method. The characteristic properties of the PVA/TiO₂ composite polymer membrane were investigated by thermal gravimetric analysis (TGA), a scanning electron microscopy (SEM), a micro-Raman spectroscopy, a methanol permeability measurement and the AC impedance method. An alkaline direct alcohol (methanol, ethanol and isopropanol) fuel cell (DAFC), consisting of an air cathode based on MnO₂/C inks, an anode based on PtRu (1:1) black and a PVA/TiO₂ composite polymer membrane, was assembled and examined for the first time. The results indicate that the alkaline DAFC comprised of a cheap, non-perfluorinated PVA/TiO₂ composite polymer membrane shows an improved electrochemical performances. The maximum power densities of alkaline DAFCs with 4 M KOH + 2 M CH₃OH, 2 M C₂H₅OH and 2 M isopropanol (IPA) solutions at room temperature and ambient air are 9.25, 8.00, and 5.45 mW cm⁻², respectively. As a result, methanol shows the highest maximum power density among three alcohols. The PVA/TiO₂ composite polymer membrane with the permeability values in the order of 10⁻⁷ to 10⁻⁸ cm² s⁻¹ is a potential candidate for use on alkaline DAFCs.     

Catalytic and DRIFTS study of the WGS reaction on Pt-based catalysts

The water–gas shift (WGS) activity of Pt/SiO₂, Pt/CeO₂ and Pt/TiO₂ catalysts was studied by in-situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). Samples contained a similar amount of Pt, between 0.34 and 0.50%, and were characterized by employing a variety of physical and spectroscopic techniques. The catalyst activities were evaluated through both CO conversion versus temperature and CO conversion versus time tests. The DRIFTS spectra were obtained on stream during the WGS reaction at increasing temperatures, from 303 to 573 K. Reduced ceria was the only active support and promoted the WGS reaction on surface bridging OH groups that react with CO to form formate intermediates. Pt/SiO₂ was more active than CeO₂ and catalyzed the WGS reaction through a monofunctional redox mechanism on metallic Pt sites. The CO conversion turnover rate was more than one order of magnitude greater on Pt/CeO₂ than on Pt/SiO₂ showing that the reaction proceeds faster via a bifunctional metal-support mechanism. Platinum on Pt/CeO₂ increased the concentration of OH groups by increasing the ceria reduction extent and also provided a faster pathway for the formation of formate intermediates in comparison to CeO₂ support. Pt/TiO₂ catalysts were clearly more active than Pt/CeO₂. The WGS reaction on Pt/TiO₂ was catalyzed via a bifunctional metal-support mechanism, probably involving the activation of CO and water on the metal and the support, respectively. The role of platinum on Pt/TiO₂ was critical for promoting the reduction of Ti⁴⁺ ions to Ti³⁺ which creates oxygen vacancies in the support to efficiently activate water.     

Effect of support and reduction temperature in the hydrogenation of CO2 over the Cu–Pd bimetallic catalyst with high Cu/Pd ratio

Metal-support interaction and catalyst pretreatment are important for industrial catalysis. This work investigated the effect of supports (SiO₂, CeO₂, TiO₂ and ZrO₂) for Cu–Pd catalyst with high Cu/Pd ratio (Cu/Pd = 33.5) regarding catalyst cost, and the reduction temperatures of 350 °C and 550 °C were compared. The activity based on catalyst weight follows the order of Si > Ce > Zr > Ti when reduced at 350 °C. The reduction temperature leads to the surface reconstruction over the SiO₂, CeO₂ and TiO₂ catalysts, while results in phase transition over Cu–Pd/ZrO₂. The effect of reduction temperature on catalytic performance is prominent for the SiO₂ and ZrO₂ supported catalysts but not for the CeO₂ and TiO₂ ones. Among the investigated catalysts, Zr-350 exhibits the highest methanol yield. This work reveals the importance of the supports and pretreatment conditions on the physical-chemical properties and the catalytic performance of the Cu–Pd bimetallic catalysts.     

Enhanced methane electrooxidation by ceria and nickel oxide impregnated perovskite anodes in solid oxide fuel cells

A key challenge preventing the full utilization of the electrochemical work potentials of hydrocarbon fuels in solid oxide fuel cells (SOFCs) is the prevalence of partial hydrocarbon electrooxidation at the anode and the resultant catalytic deactivation by coking. CeO₂–NiO impregnated La_0.3Sr_0.5TiO_3-δ (LST_A-) anodes solve both issues. These anodes exhibit 2-fold increase in the exchange current density (i_o) for CH₄ electrooxidation compared to CeO₂ impregnated NiO-YSZ (yttria-stabilized-zirconia) anodes. The presence of metal support interactions between Ni–CeO_2-δ along with the oxygen vacancies in LST_A- and CeO_2-δ enabled fast oxidation of carbon species and resulted in reduced coking. The uses of this anode in an electrolyte supported full cell configuration yielded a maximum power density of 490 mW cm⁻² in CH₄ at 1173 K.     

Methanol oxidation on hybrid catalysts: PtRu/C nanostructures promoted with cerium and titanium oxides

Hybrid catalysts comprising of ceramic, metal, and carbon phase were synthesized by incorporating titanium and cerium oxides into PtRu/C commercial catalyst using an in-situ combustion followed by heat treatment at 600 °C. The structure dependent electrochemical behavior of as-synthesized and heat-treated materials towards methanol oxidation, carbon dioxide (CO) tolerance and chemical stability was studied by XRD, HRTEM, BET, EDS, cyclic voltammetry, chronoamperometry, and CO-stripping method. As a result of heat treatment, amorphous phase of metal oxides was transformed into a crystalline phase with particle size of about 3–7 nm. Improved methanol oxidation activity of the hybrid catalysts was compared to PtRu/C catalyst as a baseline and explained by the changes in Pt electronic behavior and excess adsorption of OH-ions. When heat-treated at 600 °C, CeO₂-PtRu/C demonstrated the highest mass activity of 580 mA/mg (∼3×  that of PtRu/C) compared to TiO₂-PtRu/C (394 mA/mg). Heat-treated hybrid catalysts exhibited higher methanol oxidation activity at higher peak potentials than the corresponding as-synthesized materials. However, as-synthesized hybrid catalysts display higher CO-tolerance, lower CO-oxidation onset potentials, and better chemical stability in comparison to corresponding heat-treated catalysts. To explain the difference, a mechanism for ceramic oxide structure dependent electrochemical behavior of the hybrid catalysts is proposed and discussed.     

Continuous hydrogen production activity over finely dispersed Ag2O/TiO2 catalysts from methanol:water mixtures under solar irradiation: A structure–activity correlation

Ag₂O/TiO₂ catalysts with varying amounts of Ag₂O 0.5, 1, 2, and 5 wt% loadings are prepared by impregnation method and Ag/TiO₂ catalyst is prepared by photo deposition method. These catalysts are characterized by XRD, SEM-EDAX, DRS, XPS and TEM techniques. DRS studies clearly showing the expanded photo response of TiO₂ into visible region on impregnation of Ag⁺ ions on surface layers of TiO₂ due to the increased number of energy states created by the silver ions in TiO₂ surface lattice. TEM images are showing the fine dispersion of silver particles on TiO₂ surface. XPS of Ag₂O/TiO₂ calcined and used catalysts along with Ag₂O/TiO₂ reduced and Ag/TiO₂ photo deposited catalysts are compared and the binding energy values of Ti 2p, O1s and Ag 3d are confirming that silver ions are in interaction with TiO₂ in Ag₂O/TiO₂ calcined catalysts. EDAX analysis supports the presence of silver species on the surface layers of TiO₂. Photocatalytic hydrogen production activity studies are conducted over Ag₂O/TiO₂, Ag₂O/TiO₂ reduced and Ag/TiO₂ photo deposited catalysts in pure water and methanol:water mixtures under solar irradiation. Maximum hydrogen production of 145 μmoles/h is observed on 0.5wt% Ag₂O/TiO₂ catalyst in pure water and the maximum hydrogen production of 3350 μmoles/h is observed on 1wt% Ag₂O/TiO₂ catalyst in methanol:water mixtures. Whereas Ag₂O/TiO₂ reduced and Ag/TiO₂ photo deposited catalysts are not showing any hydrogen production activity either in water or in methanol:water mixtures under solar irradiation. Based on the XPS, DRS, TEM, SEM-EDAX studies and the hydrogen production activity on these catalysts, a structure–activity correlation has been proposed wherein the interacted Ag⁺ ions on the surface layers of TiO₂ are playing an important role in maintaining the hydrogen production activity under solar irradiation.