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Article

Enhanced Photocatalytic Hydrogen Generation from Methanol Solutions via In Situ Ni/Pt Co-Deposition on TiO2

by
Mst. Farhana Afrin
1,*,
Mai Furukawa
1,
Ikki Tateishi
2,
Hideyuki Katsumata
1,
Monir Uzzaman
1,* and
Satoshi Kaneco
1,*
1
Department of Applied Chemistry, Graduate School of Engineering, Mie University, Tsu 514-8507, Mie, Japan
2
Mie Global Environment Center for Education & Research, Mie University, Tsu 514-8507, Mie, Japan
*
Authors to whom correspondence should be addressed.
J. Compos. Sci. 2025, 9(2), 68; https://doi.org/10.3390/jcs9020068 (registering DOI)
Submission received: 15 October 2024 / Revised: 22 January 2025 / Accepted: 24 January 2025 / Published: 2 February 2025
(This article belongs to the Special Issue Feature Papers in Journal of Composites Science in 2024)
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Abstract

:
TiO2 is widely utilized as an excellent photocatalyst in energy production. However, its rapid electron and hole recombination confers poor photocatalytic activity. Cocatalysts are essential for increasing photocatalytic efficacy by introducing improved electron transmission and enlarging the active site. Herein, the photocatalytic degradation of aqueous methanol solution to generate hydrogen was studied with the simultaneous in situ deposition of metals (M = Ag, Cu, Ni, Pd, and Pt) on the TiO2 surface. Adding methanol to water and incorporating a bimetallic cocatalyst enhanced hydrogen production by reducing the electron–hole pair recombination. The studied metal ions could be reduced by the conduction band electrons of TiO2 for the in situ simultaneous deposition of metal. The larger work function value of the studied metals favored the Schottky junction formation, which contributed to increasing photocatalytic efficiency. Among these simultaneous metal-deposited photocatalysts, maximal photocatalytic hydrogen production was achieved with NiPt/TiO2. The optimal component was 0.01 wt.% Ni/1.0 wt.% Pt for TiO2. The hydrogen evolution with NiPt/TiO2 was approximately 341 and 1.3 times better than that with pure TiO2 and Pt/TiO2, respectively. A potential reaction pathway for photocatalytic hydrogen production from an aqueous methanol solution over NiPt/TiO2 photocatalyst has also been proposed.

1. Introduction

Clean, sustainable, and inexpensive energy sources are highly sought after to fulfill energy requirements and to save the Earth from pollution [1]. Hydrogen (H2) is preferred over non-renewable fossil fuels due to its eco-friendly and cost-effective properties [2]. Compared to hydrocarbon fuels, H2 has a 2.75-fold greater energy output (122 kJ/g) efficiency [3]. H2 can be produced by employing many processes, including thermochemical, electrochemical, photochemical, photocatalytic, and photo-electrochemical processes [4], and it can be derived from water and other carbonaceous substances such as natural gas and biomass [5]. Its natural scarcity and the requirement for low-cost manufacturing techniques are the main issues with using H2 gas as fuel. Currently, around 5% of commercial hydrogen is produced from renewable sources, while the remaining portion is still produced from fossil fuels [6].
Liquid sunshine refers to the combination of sunshine energy with CO2 and water to generate green liquid fuels such as methanol [7]. Methanol is utilized directly as fuel when mixed with petrol, in addition to being used as a raw material in different chemical syntheses [8]. Methanol is seen as the most promising hydrogen fuel source option among other high-energy-density liquid fuels [9]. Several processes, such as steam reforming [10], direct dehydrogenation [11], partial oxidation [12], decomposition [13], oxidative reforming [14], and photocatalytic oxidation [15,16], have previously been suggested for the conversion of aqueous methanol to hydrogen. Considering its feasible and affordable energy generation, photocatalytic hydrogen generation with the degradation of aqueous methanol may become a promising technique.
In the field of energy conversion and environmental restoration, titanium dioxide (TiO2) is thought to be the most advantageous photocatalyst due to its excellent photoreactivity, nontoxicity, eco-friendliness, abundance, cheapness, long-term stability, and resilience against chemical and photochemical corrosion in aggressive aqueous solutions [17,18]. The photocatalytic reaction starts with the absorption of energy equal to or larger than the bandgap. The photogenerated electrons are promoted from the valance band (VB) to the conduction band (CB) and create an electron–hole (e−/h+) pair. These photogenerated electrons can reduce H+ to H2, and holes on the semiconductor surface can degrade the H2O into O2 and H+. Due to the wide energy bandgap of pure TiO2 (3.20 eV), it requires a higher amount of energy for the electronic transition from VB to CB [19]. The photocatalytic efficiency of semiconductor-based photocatalysts can be significantly influenced by crystal structure, surface area, surface hydroxyl density, porosity, and size [20]. The reduced performance of pure TiO2 under visible light irradiation (380 nm) in hydrogen production from pure water has already been reported [21]. Different methods, including noble metal loading, metal ion doping, composite formation, and surface modification, have been employed to enhance their efficiencies [22]. Noble metal (Ag, Au, and Pt) deposition on a photocatalyst (TiO2) enhances hydrogen generation by moving the photogenerated electrons from the semiconductor CB to the doping metals and by reducing the recombination rate with holes [9,22,23,24,25,26,27]. In addition, some Earth-abundant metal dopants (Cu, Ni, Fe, and Co) and bimetallic systems have been reported to be efficient cocatalysts for TiO2 in photocatalytic hydrogen production from methanol [9,28,29,30]. Moreover, the utilization of metal oxides (CuO, ZnO, Al2O3, Fe2O3, Ag2O, CoO, SnO2, and NiO) along with TiO2 also enhanced photocatalytic hydrogen production from aqueous methanol solution [10,31,32,33,34,35].
However, the recombination of photogenerated electrons and holes has been a pervasive issue for photocatalytic hydrogen production. Using organic substances as electron donors, which react irreversibly with photogenerated holes, is another efficient way to prevent the fast recombination of photogenerated electrons with holes. During the photocatalytic hydrogen generation process, a wide range of organic compounds, including alcohols [36,37], organic acids [38,39,40], organic pollutants [41,42,43], starch, and glucose [44], have been successfully employed as electron donors. Specifically, the addition of methanol (an electron donor) as a hole scavenger significantly increases hydrogen evolution [28,45].
The present research focused mainly on photocatalytic hydrogen production from an aqueous methanol solution with in situ simultaneous bimetal (Ni and Pt) deposition on nanocrystalline TiO2. For comparison with in situ simultaneous bimetal deposition, the photocatalytic performance of AgPt/TiO2, PdPt/TiO2, and CuPt/TiO2 was evaluated.

2. Materials and Methods

2.1. Chemicals and Materials

All the reagents were of analytical grade and used as received without further purification. Photocatalyst titanium oxide (TiO2 P-25) was supplied by Degussa Co., Ltd., Frankfurt, Germany (80% anatase and 20% rutile, surface area 50 m2 g−1, and average particle size 30 nm). Methanol (99.8%) was supplied by Nacalai Tesque, Inc., Kyoto, Japan. A standard stock solution of metal ion (1000 mg L−1) was purchased from Fujifilm Wako Pure Chemicals, Osaka, Japan, and Sigma-Aldrich, Tokyo, Japan.

2.2. Photocatalytic Hydrogen Production Reaction

All the photocatalytic hydrogen production experiments with TiO2 were conducted in a heat-resistant Pyrex glass vessel reactor with a 55.6 mL inner volume at 50 °C using an aqueous solution (30 mL) containing methanol (10 vol%). Cocatalyst metal ions could be reduced at the photocatalyst surface through the in situ photodeposition. A 15 W black lamp with an emission of about 352 nm (Toshiba Lighting & Technology Corp., Tokyo, Japan) was used to irradiate the reaction mixture for 3 h. The light intensity was measured by a UV radio meter (UIT-201, Ushio Inc., Tokyo, Japan), and the value was 0.6 mW cm−2. The reaction mixture was continuously stirred for the continuous dispersion of photocatalysts in the aqueous methanol solution during the irradiation. The reactor temperature was kept constant at 50 °C using a hot magnetic stirrer. A 250 µL syringe (ITO, Co., Ltd., Tokyo, Japan) was utilized to collect the evolved hydrogen and analyzed by gas chromatography (GL Sciences, GC-3200, Tokyo, Japan) equipped with a thermal conductivity detector (GC-TCD). The temperature of the injector, column, and detector was maintained at 50 °C. A stainless column (4 m, 2.17 mm inner diameter) packed with a Molecular Sieve 5A (mesh, 60–80) was utilized for the separation. Argon (99.9%) with a 7.0 mL min−1 flow rate was used as a carrier gas. A 250 µL gas sample was injected to GC-TCD, maintaining the 15 min analyzing time. To enhance the photocatalytic hydrogen production, some metal ions (Ag, Ni, Cu, and Pd) were simultaneously deposited on the TiO2 photocatalyst along with Pt.

3. Results and Discussion

3.1. Photocatalytic Hydrogen Production

The unpropitious issues in photocatalytic hydrogen production, such as fast electron–hole pair recombination rate and larger energy bandgap, can be overcome by using a hole scavenger agent and doping metals with the photocatalyst. In this study, both the hole scavenger methanol agent and the in situ simultaneous deposition of a co-metal catalyst were employed in photocatalytic hydrogen generation. No hydrogen was detected in the photolysis reaction (absence of catalyst). Meanwhile, a trace amount of H2 was detected in the catalysis (dark condition) reaction. The work function value of metal significantly influences the Schottky junction effect at the metal–TiO2 interface. A larger work function can increase the Schottky barrier effect by reducing further electron–hole recombination. As a result, metals with appropriate work functions can facilitate electron transfer, assist in overcoming the Schottky energy barrier, and lead to enhanced photocatalytic efficiency. The work functions of the reported metals Pt, Ni, Pd, Cu, and Ag are 5.65, 5.25, 5.12, 4.65, and 4.26 eV, respectively, and are greater than that of TiO2 (4.2~4.5 eV) [46,47,48].

3.2. Effect of Pt Loading

Among the studied cocatalysts, Pt is considered to be the most efficient for hydrogen evolution because the Gibbs free energy of adsorbed atomic hydrogen is close to zero, making it thermodynamically favorable for H2 binding and release. Pt has a large work function (5.65 eV) and a lower overpotential for the reduction of H+ into H2 [49]. The Pt loading impact on TiO2 in photocatalytic hydrogen generation from aqueous methanol solution is presented in Figure 1. Due to the Pt deposition on the TiO2 surface, the photogenerated excited electrons of TiO2 migrate into Pt and easily form a Schottky junction between the electrons, which immediately reduce Pt4+ to Pt0 [50]. The Pt cocatalyst could potentially hinder the electron−hole recombination [51]. As shown in Figure 1a, a very small amount of hydrogen was produced by the bare TiO2 photocatalytic reaction (0.7 µmol) due to the fast electron–hole pair recombination. H2 production increased 267-fold due to the addition of 1.0 wt.% Pt (187 µmol). These results indicate the improvement in photocatalytic performance by reducing the bandgap and electron–hole pair recombination rate. The optimum Pt loading value was the same as that reported in a previous study [52]. A similar link between photocatalytic activity and the Pt loading amount has been demonstrated by earlier research [51,53].

3.3. Effect of Ag/Pt Loading

The effect of the simultaneous bimetallic in situ deposition of Ag and Pt on the TiO2 surface in photocatalytic hydrogen production from aqueous methanol solution is presented in Figure 1b. Different amounts of Ag and 1.0 wt.% Pt were simultaneously photodeposited on the TiO2 photocatalyst surface to optimize the amount of Ag loading. As shown in Figure 1b, with 0.01 wt.% of Ag and 1.0 wt.% Pt, the hydrogen production slightly decreased (180 µmol) compared to Pt/TiO2-assisted production. Since the work function value of Ag (4.26 eV) is smaller than that of TiO2 (4.2~4.5 eV), the photocatalyst was not favorable for establishing a Schottky junction between Ag and TiO2, leading to the backflow of injected electrons from TiO2 to Ag [48]. Further, an increase in Ag loading (1.0 wt.%) almost stopped hydrogen production due to the coagulation of cocatalysts, poor dispersion, and blockage of incident light on the photocatalyst surface [54,55].

3.4. Effect of Cu/Pt Loading

Cu-doped TiO2 photocatalytic hydrogen production has been widely reported. Herein, the effect of Cu doping on CuPt/TiO2 photocatalytic hydrogen production from aqueous methanol solution under black light irradiation at 50 °C (Figure 2) was investigated. With the addition of 0.01 wt.% Cu into the Pt (1.0%)/TiO2, a 1.25-fold higher amount of hydrogen evolved compared to Pt/TiO2. Due to Cu having a relatively larger work function (4.65 eV) than that of semiconductor TiO2 (4.2~4.5 eV), a Schottky junction can form between Cu and TiO2 and reduce electron–hole recombination. In contrast, with a further increase in Cu content from 0.01 wt.% to 1.0 wt.%, the hydrogen production dropped rapidly from 234 to 107 µmol due to the light filtration from excess metal deposition, the partial blockage of catalyst active sites, and the formation of recombination centers by excessively deposited metal ions [16]. Previous research has shown a similar relationship between photocatalytic activity and Cu loading quantity [20,56].

3.5. Effect of Ni/Pt Loading

The effect of the Ni loading concentration on the photocatalytic hydrogen generation activity with NiPt/TiO2 from aqueous methanol solution was studied (Figure 3). The formation of Ni/TiO2 demonstrated the mesoporous material with a substantially larger surface area and a narrower pore distribution [57]. Wang et al. first reported the hydrogen production from aqueous methanol solution due to the adsorption of Ni2+ on the surface of TiO2 [58]. Biswas et al. reported enhanced hydrogen production from aqueous methanol solution using TiO2 decorated with Ni and Pt. Pt may be present to promote the photoreduction of Ni2+ to Ni0 and prevent Ni(OH)2 formation [50]. The photogenerated electrons preferentially reduce Pt4+ to Pt0 on the surface of TiO2 in the presence of Ni2+ and Pt4+, since the redox potential of Pt4+ (Pt4+/Pt0, E0 = 1.44 V) is positive to the Ni2+ (Ni2+/Ni0, E0 = −0.257 V). With an increase in the Ni content from 0.005 wt.% to 0.01 wt.%, the hydrogen production gradually increased from 150 to 239 µmol. Because Pt (5.65 eV) and Ni (5.25 eV) have larger work function values than TiO2 (4.2~4.5 eV), both catalysts can contribute to establishing a Schottky junction between Pt-TiO2 and Ni-TiO2 and suppress the backflow of electrons from the semiconductor to metals. Pt and Ni cocatalysts may collaboratively boost the photocatalytic activity, owing to the efficient interfacial charge transfer and prolonged lifetime of charge carriers [49]. With the further increase in Ni deposition from 0.01 to 0.1 wt.%, the hydrogen production rapidly decreased from 239 to 150 µmol. The deposition of an excess amount of cocatalyst in a photocatalytic reaction decreases the active surface area of TiO2 because it occupies most of the surface area with cocatalysts and obstructs incident light [59].

3.6. Comparison of Metallic Properties on the Photocatalytic Hydrogen Production

To assess the metal ions insertion effect, photocatalytic hydrogen production reactions were conducted with the simultaneous in situ bimetallic deposition on TiO2. The redox potentials of Pd(II), Ag(I), [PtCl6]2−/[PtCl4]2−, [PtCl4]2−/Pt, Cu(II), and Ni(II) are 0.951, 0.799, 0.680, 0.755, 0.342, and −0.257 V vs. standard hydrogen electrode (SHE), respectively [60]. If the semiconductor’s conduction band becomes more negative than the metal ion’s reduction potential in the system, conduction band electrons can reduce the metal ion. The conduction band and valence band edges for TiO2 photocatalyst are −0.46 V and +2.7 V vs. SHE (pH = 7), respectively [61]. Therefore, the photodeposition of Pd2+, Ag+, Ptn+, Cu2+, and Ni2+ can occur during the photocatalytic hydrogen production process, and their reduction to the metals is also a thermodynamically favorable reaction [16,46]. The photodeposited metal ions on the photocatalyst surface contribute to moving the Fermi level to more significant negative potentials. The shift in Fermi level enhances the energetics of the composite system and increases the interfacial charge transfer process [49,62,63]. Gnanamani et al. also tested photocatalytic H2 production using M-TiO2 (M = Pt, Pd, Cu, Ru, Ag) from 10 vol.% CH3OH/H2O under UV light. The tested material activities were as follows: Pt-TiO2 > Pd-TiO2 > Cu-TiO2 > Ru-TiO2 > Ag-TiO2 > TiO2 [64]. For instance, Kominami et al. fabricated Au–TiO2–M (M = Pt, Pd, Ru, Rh, Au, Ag, Cu, and Ir) and found that the H2 generation rate from 2-propanol using the Au–TiO2–M photocatalyst depended on the type of M, decreasing in the following order: Pt > Pd > Ru > Rh > Au > Ag > Cu > Ir [65].
To compare the hydrogen production efficiency from aqueous methanol solution with the simultaneous in situ bimetallic deposition on the TiO2 surface, the investigated results are summarized in Table 1. Table 1 demonstrates that the amount of hydrogen evolution increased in the sequence Pd < Ag < Cu < Ni, with the highest production achieved for Ni2+ (0.01 wt.%) deposition. Ag deposition decreased H2 production due to insufficient interfacial charge transfer. Although the redox potential and work function values were favorable, the hydrogen production decreased with 0.01 wt.% of Pd deposition on the Pt/TiO2 surface. Abdullah et al. reported that the application of 0.6 wt.% Pd significantly promoted electron transfer from the conduction band of TiO2 to the metals [66]. Chen et al. achieved the highest hydrogen from an aqueous ethanol solution using 1.0 wt.% Pd/TIO2 [67].
From Table 1, the amount of hydrogen evolved from the Pt (1.0 wt.%)/TiO2 photocatalytic reaction was 260 times higher (3117 µmol g−1 h−1) than the pure P-25 TiO2 (12 µmol g−1 h−1). The highest amount of hydrogen was achieved from the Ni (0.01 wt.%)/Pt (1.0 wt.%)/TiO2 photocatalytic reaction (3983 µmol g−1 h−1) owing to the establishment of the Schottky barrier and prolonging the lifetime of the charge carrier.

3.7. Proposed Mechanism

To better understand the bimetallic NiPt/TiO2 photocatalytic hydrogen production from the aqueous methanol solution, a reaction mechanism is shown in Figure 4. Electron–hole pairs are produced on the TiO2 surface due to UV light irradiation. Additionally, photogenerated electrons in the valance band are stimulated to the conduction band, leading to the availability of photogenerated holes in the VB (Figure 4). These promoted photogenerated electrons can reduce H+ into H2, and holes on the semiconductor surface can decompose H2O into O2 and H+ [68]. This process involves a reduction with the available electrons in the conduction band and the oxidation of H2O by holes in the valence band. Owing to the doping of transition and noble metals into TiO2, the bandgap can be reduced by making the quasi-static energy level of the dopants be between the conduction and valance band, and the doping of the cocatalyst can decrease the charge carrier recombination rate [69]. With the reduction in the TiO2 bandgap, the photon absorption capability for the materials increased, resulting in the improvement in the formation of electron and hole pairs [70]. The use of Pt may prevent the deposition of Ni(OH)2 and enhance the migration of electrons from the TiO2 surface to Ni2+. Herein, in the presence of Ni2+ and Pt4+, the photogenerated electrons preferentially reduce Pt4+ to Pt0 at the surface active site of TiO2 due to the favorable redox potential of Pt4+ (Pt4+ /Pt0, E0 = 1.44 V) compared to Ni2+ (Ni2+/Ni0, E0 = −0.257 V). A Schottky junction forms immediately after the deposition of Pt nanoparticles on the TiO2 surface and enhances the migration of photogenerated electrons from the CB of TiO2 to Pt. Ni2+ is reduced to Ni0 by the electrons from the Pt surface. Hence, Ni nanoparticles prolonged the charge carrier lifetime by charge migration through the Ni-Pt interface [50]. Some previous reports show the following:
NiPt/TiO2 + hν → e− (NiPt) + h+ (TiO2)
h+ + H2O → H+ + •OH
2e− + 2H+ → H• + H• → H2
H2O + 1.23 eV (hν) → H2 + 1/2O2
To hinder the faster electron–hole recombination, the sacrificial agent (methanol) was employed to keep the separation of photogenerated electrons and holes from the recombination. Water splitting is an endothermic reaction, and methanol has a lower splitting energy than water. The photogenerated hole of TiO2 can oxidize methanol and release H+ and •CH2OH, which can further produce formaldehyde (Equations (6) and (7)). Formic acid is produced due to the oxidation of formaldehyde in the presence of •OH radical and photogenerated holes (Equation (9)). Finally, HCOOH undergoes decarboxylation to produce hydrogen and CO2 following the photo-Kolbe reaction (Equations (10) and (11)). The enhanced hydrogen production may be attributed to the interaction between a charge transfer capability and the adsorption activity of protons for the simultaneous deposition of cocatalyst Pt and Ni on the TiO2 surface. Biswas, S. et al. [50], Chen, W. T. et al. [71,72], Melián, E. P. et al. [73], and Jing, D. et al. [57] reported improved H2 production activity from the aqueous solution of different alcohols with Ni/TiO2, where Ni2+ acts as shallow trapping sites, significantly increasing the photocatalyst’s activity, which is consistent with the current study.
CH3OH + h+ → H+ + •CH2OH
•CH2OH + h+ → H+ + HCHO
2e− + 2H+ → H2
HCHO + •OH + h+ → H+ + HCOOH
HCOOH → H+ + HCOO−
HCOO− + 2h+ → H+ + CO2
2e− + 2H+ → H2
Hori et al. reported the electrochemical reduction of CO2 at metal electrodes in aqueous media and detected various products, such as CO, HCOO−, CH4, C2H4, H2, and alcohol [74]. The yield and type of reduction products can depend strongly on the electrode metal. According to Hori et al., the electrode metals can be grouped according to product selectivity: (1) hydrocarbons: Cu; (2) carbon monoxide: Au, Ag, Zn, Pd, and Ga; (3) formic acid: Pb, Hg, In, Sn, Cd, and Tl; and (4) hydrogen: Ni, Fe, Pt, and Ti. In the Pt and Ni electrodes, H2 evolved as the major product.
The Schottky junction formation based on the work function value is in the order of Pt > Ni > Pd > Cu > Ag [46,47,48], and the hydrogen evolution potential of the utilized metals is in the order of Pd > Pt > Ni > Cu > Ag (Table 2) [74].

4. Conclusions

In summary, photocatalytic hydrogen production from aqueous methanol solution with the in situ simultaneous photodeposition of bimetals (Ag, Cu, Ni, Pd, and Pt) onto TiO2 was investigated at 50 °C. The redox potential values confirmed that TiO2 can reduce the investigated metals for the deposition of metals onto the photocatalyst surface. Consequently, having a larger work function value than TiO2, Pt, Ni, Pd, and Cu can form a Schottky junction on the semiconductor surface, accelerating the interfacial charge transfer and photocatalytic efficiency. Similarly, the selective hydrogen formation tendency of Ni and Pt was relatively higher than that of other studied metals. The incorporation of metals significantly enhanced hydrogen production, and the best production was achieved under 0.01 wt.% Ni/1.0 wt.% Pt/TiO2 reaction conditions under UV light irradiation. Under optimal conditions, the photocatalytic hydrogen production with bimetallic (Ni, Pt) deposition on the TiO2 surface increased 341-fold compared to those obtained with sole TiO2. The insertion of Ni and Pt on TiO2 increased the interfacial charge transfer efficiency and the addition of an aqueous methanol solution as an electron donor suppressed electron–hole pair recombination.

Author Contributions

M.F.A.: formal analysis, investigation, writing—original draft, review and editing. M.U.: formal analysis, methodology, visualization, writing—original draft, review and editing. M.F.: formal analysis, review and editing. I.T.: formal analysis, review and editing. H.K.: writing, review and editing. S.K.: conceptualization, writing—review and editing and supervision. All authors have read and agreed to the published version of the manuscript.

Funding

This research was partially funded by Grant-in-Aid for Scientific Research (B) 21H03642 from the Ministry of Education, Culture, Sports, Science and Technology of Japan.

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors acknowledge Yukiko Fujita for her support.

Conflicts of Interest

All authors have declared that (i) no support, financial or otherwise, has been received from any organization that may have an interest in the submitted work; (ii) there are no other relationships or activities that could appear to have influenced the submitted work. All experiments were conducted at Mie University. Any opinions, findings, conclusions, or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the supporting organizations.

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Figure 1. Effect of in situ simultaneous deposition of (a) Pt and (b) Ag on TiO2 for hydrogen production from aqueous methanol solution.
Figure 1. Effect of in situ simultaneous deposition of (a) Pt and (b) Ag on TiO2 for hydrogen production from aqueous methanol solution.
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Figure 2. Effect of in situ simultaneous Pt and Cu deposition on photocatalytic hydrogen production with TiO2 from aqueous methanol solution for 3 h.
Figure 2. Effect of in situ simultaneous Pt and Cu deposition on photocatalytic hydrogen production with TiO2 from aqueous methanol solution for 3 h.
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Figure 3. Effect of in situ simultaneous Pt and Ni deposition on photocatalytic hydrogen production with TiO2 from aqueous methanol solution for 3 h.
Figure 3. Effect of in situ simultaneous Pt and Ni deposition on photocatalytic hydrogen production with TiO2 from aqueous methanol solution for 3 h.
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Figure 4. Reaction mechanism of photocatalytic hydrogen production from the aqueous methanol solution using the TiO2 photocatalyst with the simultaneous photodeposition of Ni and Pt.
Figure 4. Reaction mechanism of photocatalytic hydrogen production from the aqueous methanol solution using the TiO2 photocatalyst with the simultaneous photodeposition of Ni and Pt.
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Table 1. Comparison of photocatalytic hydrogen production.
Table 1. Comparison of photocatalytic hydrogen production.
Photocatalyst (wt.%)H2 Production (µmol g−1 h−1)P-25 TiO2 Ratio
P-25 TiO2121.0
Pt(1.0%)/TiO23117260
Cu(0.01%)/Pt(1.0%)/TiO23900325
Ni(0.01%)/Pt(1.0%)/TiO23983332
Pd(0.01%)/Pt(1.0%)/TiO22800233
Table 2. The work function, hydrogen evolution potential, and redox potential of the studied metals.
Table 2. The work function, hydrogen evolution potential, and redox potential of the studied metals.
MetalWork Function
(eV)		Hydrogen Evolution
Potential (V vs. SHE)		Redox Potential
(V vs. SHE) [60]
Cu4.65−0.95Cu2+/Cu (0.342)
Ni5.25−0.68Ni2+/Ni (−0.257)
Ag4.26−1.14Ag+/Ag (0.799)
Pd5.12−0.35Pd2+/Pd (0.951)
Pt5.65−0.38[PtCl6]2−/[PtCl4]2− (0.680)
[PtCl4]2−/Pt0 (0.755)
Pt4+/Pt0 (1.44)
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Afrin, M.F.; Furukawa, M.; Tateishi, I.; Katsumata, H.; Uzzaman, M.; Kaneco, S. Enhanced Photocatalytic Hydrogen Generation from Methanol Solutions via In Situ Ni/Pt Co-Deposition on TiO2. J. Compos. Sci. 2025, 9, 68. https://doi.org/10.3390/jcs9020068

AMA Style

Afrin MF, Furukawa M, Tateishi I, Katsumata H, Uzzaman M, Kaneco S. Enhanced Photocatalytic Hydrogen Generation from Methanol Solutions via In Situ Ni/Pt Co-Deposition on TiO2. Journal of Composites Science. 2025; 9(2):68. https://doi.org/10.3390/jcs9020068

Chicago/Turabian Style

Afrin, Mst. Farhana, Mai Furukawa, Ikki Tateishi, Hideyuki Katsumata, Monir Uzzaman, and Satoshi Kaneco. 2025. "Enhanced Photocatalytic Hydrogen Generation from Methanol Solutions via In Situ Ni/Pt Co-Deposition on TiO2" Journal of Composites Science 9, no. 2: 68. https://doi.org/10.3390/jcs9020068

APA Style

Afrin, M. F., Furukawa, M., Tateishi, I., Katsumata, H., Uzzaman, M., & Kaneco, S. (2025). Enhanced Photocatalytic Hydrogen Generation from Methanol Solutions via In Situ Ni/Pt Co-Deposition on TiO2. Journal of Composites Science, 9(2), 68. https://doi.org/10.3390/jcs9020068

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