Catalytic oxidation of methanol on molybdate-modified platinum electrode in sulfuric acid solution

The catalysis of methanol oxidation on molybdate-modified platinum was studied by using linear sweep voltammetry (LSV), cyclic voltammetry (CV) and chronoamperometry in the solutions with H₂SO₄ concentrations from 0.5 to 4.5 M. It was found that methanol oxidation was catalyzed on the modified platinum by lowering methanol oxidation potential and promoting methanol oxidation current. There was the strongest catalysis in 3.7 M H₂SO₄ solution. In this solution, methanol oxidation took place on the modified platinum at the potential 0.2 V more negatively than on the non-modified platinum and the steady oxidation current of methanol on the modified platinum at 0.7 V versus SCE was 10 times that on the non-modified platinum. Molybdates were reduced to adsorbed hydrogen molybdenum(IV) bronzes on platinum in H₂SO₄ solution at a very negative potential. The amount of reduced molybdates decreased with decreasing H₂SO₄ concentrations. The reduced molybdates were oxidized to different forms of hydrogen molybdenum bronzes (H_xMoO₃, 0<x<2) depending on the H₂SO₄ concentration. Platinum was modified by these hydrogen molybdenum bronzes, but under-modified in the solution with lower H₂SO₄ concentration and over-modified in the solution with higher H₂SO₄ concentration. The catalysis of methanol oxidation was weakened when the platinum was under- or over-modified.     

(In,Cu) Co-doped ZnS nanoparticles for photoelectrochemical hydrogen production

In and Cu co-doped ZnS nanoparticles were successfully synthesized in DI water and ethanol solvent by a sonochemical approach using citric acid as surfactants in aqueous medium. FESEM micrographs show that In and Cu co-doped ZnS crystallites have a rough surface nanostructure and the as-synthesized photocatalysts were tested for the photocatalytic hydrogen evolution from water splitting via the irradiation of simulated sunlight. Among In and Cu co-doped ZnS products, 4In4CuZnS photocatalyst can achieve the maximum hydrogen production rate (752.7 μmol h⁻¹ g⁻¹) in 360 min under simulated sunlight illumination. Meanwhile, we separated the hydrogen and oxygen cells using an ion exchange membrane. Both electrodes (working electrode and Pt electrode) are dipped into each cell containing an aqueous solution containing 0.1 M Na₂S at pH 3 to convert water into hydrogen and oxygen under solar irradiation. As expected, the photoelectrochemical water splitting cells could significantly improve the photocatalytic activity, where the 4In4CuZnS nanoparticles shows the photoelectrochemical performance with photocurrent density of 12.2 mA cm⁻² at 1.1 V and hydrogen evolution rate of 1189.4 μmol h⁻¹ g⁻¹.     

Photocurrent and photoelectrochemical hydrogen production with tin porphyrin and platinum nanowires immobilized with nafion on glassy carbon electrode

Platinum nanowires mixed with Tin meso-tetra (4-pyridyl) porphine dichloride and nafion solution was used to modify the surface of glassy carbon electrode for photocurrent generation and photo-electrochemical hydrogen production. Different concentrations of porphyrin (50 μM, 100 μM, 300 μM and 500 μM) and platinum loading (200 μg/cm², 400 μg/cm², 600 μg/cm² and 800 μg/cm²) were tested at −150 mV Vs Ag/AgCl in reaction cell containing the modified glassy carbon electrode as working electrode, platinum wire as counter electrode and Ag/AgCl as reference electrode, under illumination to determine the optimum, based on photocurrent production in 50 mM potassium hydrogen phthalate buffer (pH 3) containing 0.1Na₂SO₄ as supporting electrolyte. Optimum photocurrent was obtained at 100 μM tin porphyrin and 600 μg/cm² platinum loading. Detectable amount of hydrogen was produced at −350 mV Vs Ag/AgCl under irradiation with visible light.     

Parametric study on electrochemical reforming of glycerol for hydrogen production

Hydrogen production by electrochemical reforming of glycerol was investigated in this study. Within this scope, the performance of the system under different operating conditions was evaluated by parametric studies and optimum operating conditions were determined. The effects of membrane type, membrane pre-treatment procedure and temperature were investigated. System performance was examined also with long-term tests. The formation of hydrogen at the cathode was determined by analyzing the product gases by gas chromatography. Optimum condition for maximum hydrogen production was obtained with the Zn/Zn electrode pair in the presence of 0.4 M glycerol and 0.04 M H₂SO₄ at the anode side, 0.04 M H₂SO₄ at the cathode side and with pre-treated Nafion XL membrane. As the result of performance tests, room temperature and 2 V potential were found to be the most suitable operating conditions.     

Effect of sodium sulfite on acid pretreatment of wheat straw with respect to its final conversion to ethanol

A pretreatment process that combines dilute acid and sodium sulfite has been applied to wheat straw to study the effect of temperature (120–180 °C) and sodium sulfite concentration (0–3%) on the yield of glucose in subsequent enzymatic hydrolysis and ethanol production by fermentation. The results were compared with both dilute acid pretreatment (without Na₂SO₃ addition) and hot water pretreatment. Formation of furfural and hydroxymethylfurural, which can inhibit ethanol-producing microorganisms, were measured and the ethanol yield in a subsequent fermentation was evaluated. The results indicate that a combination of 180 °C, 30 min, 1% H₂SO₄ and 2.4% Na₂SO₃ during pretreatment produced the highest ethanol yield; 17.3 g/100 g dry weight of initial biomass, which corresponds to 75% of the theoretical yield from glucose. 28 mg of furan inhibitors (sum of furfural and hydroxymethylfurfural) per gram dry weight of initial wheat straw were generated under this condition. Increasing sulfite loading up to 2.4% decreased inhibitor formation, leading to increased delignification and preservation of cellulose from dissolution. On the other hand, an elevated temperature in combination with low pH reduced the amount of solid phase after pretreatment, increased the level of inhibitors and reduced the concentration of ethanol produced by fermentation.     

Electrochemical conversion of enriched crude glycerol: Effect of operating parameters

The enrichment of crude glycerol (29.8 wt.%) from a biodiesel production plant and its subsequent electrochemical conversion under a galvanostatic mode to added-value compounds was successfully performed at a laboratory scale. The optimal solvent-extraction based enrichment of the crude glycerol, after the acid pre-treatment to remove most free fatty acids and salts, was found using n-propanol:pre-treated crude glycerol at volume ratio of 2, attaining 97.9% glycerol. The effects of the initial glycerol solution pH (1, 7 or 11), type of electrode (platinum (Pt), titanium-coated ruthenium oxide (Ti/RuO₂) or stainless steel (SS)) and applied current density (0.08–0.27 A/cm²) were explored. Using a galvanostatic mode, the enriched crude glycerol could be converted to added-value products, such as ethylene glycol, acetol, glycidol, acrolein, 1,2-propanediol (PD) and 1,3-PD. A Pt electrode, initial glycerol solution pH of 1 and current density of 0.14 A/cm² were found to be optimal giving a complete conversion of 0.3 M glycerol within 14 h with a total product yield of 68.7%. However, each specific product had a different optimal applied current density and electrolysis time. Finally, a simplified diagram showing the possible major reaction pathways of glycerol conversion by this electrochemical conversion over a Pt electrode was presented.     

Simultaneous production of hydrogen and ethanol from waste glycerol by Enterobacter aerogenes KKU-S1

Factors affecting simultaneous hydrogen and ethanol production from waste glycerol by a newly isolated bacterium Enterobacter aerogenes KKU-S1 were investigated employing response surface methodology (RSM) with central composite design (CCD). The Plackett-Burman design was first used to screen the factors influencing simultaneous hydrogen and ethanol production, i.e., initial pH, temperature, amount of vitamin solution, yeast extract (YE) concentration and glycerol concentration. Results indicated that initial pH, temperature, YE concentration, and glycerol concentration had a statistically significant effect (p ≤ 0.05) on hydrogen production rate (HPR) and ethanol production. The significant factors were further optimized using CCD. Optimum conditions for simultaneously maximizing HPR and ethanol production were YE concentration of 1.00 g/L, glycerol concentration of 37 g/L, initial pH of 8.14, and temperature of 37 °C in which a maximum HPR and ethanol production of 0.24 mmol H₂/L h and 120 mmol/L were achieved.     

Photocatalytic hydrogen production with CuS/ZnO from aqueous Na2S + Na2SO3 solution

The photocatalytic hydrogen production in the sacrificial S²⁻–SO₃²⁻ anions was investigated with ZnO in the addition of metal sulfides containing Ag₂S, CuS, Fe₂S₃, and NiS. In the absence of metal sulfides, the photocatalytic H₂ evolution using ZnO was observed with 255 μmol g⁻¹. The CuS amount and the concentrations of S²⁻ and SO₃²⁻ ions were optimized. It was found that ternary component semiconductor CuS/ZnS/ZnO was formed during the photocatalytic hydrogen production in the aqueous Na₂S + Na₂SO₃ solution. The photocatalytic hydrogen evolution with CuS/ZnS/ZnO in the 0.4 M Na₂S–0.4 M Na₂SO₃ solution was more than about 8.5 times better compared with those obtained with only ZnO. The CuS clusters on the surface of ZnS/ZnO seem to play an important role on the separation for electron–hole pair and the enhancement of H₂ production. Nano-sized ZnS/ZnO photocatalytic hydrogen technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy.     

Impact of regulated pH on proto scale hydrogen production from xylose by an alkaline tolerant novel bacterial strain, Enterobacter cloacae DT-1

A hydrogen producing facultative anaerobic alkaline tolerant novel bacterial strain was isolated from crude oil contaminated soil and identified as Enterobacter cloacae DT-1 based on 16S rRNA gene sequence analysis. DT-1 strain could utilize various carbon sources; glycerol, CMCellulose, glucose and xylose, which demonstrates that DT-1 has potential for hydrogen generation from renewable wastes. Batch fermentative studies were carried out for optimization of pH and Fe²⁺ concentration. DT-1 could generate hydrogen at wide range of pH (5–10) at 37 °C. Optimum pH was; 8, at which maximum hydrogen was obtained from glucose (32 mmol/L), when used as substrate in BSH medium containing 5 mg/L Fe²⁺ ion. Decrease in hydrogen partial pressure by lowering the total pressure in the fermenter head space, enhanced the hydrogen production performance of DT-1 from 32 mmol H₂/L to 42 mmol H₂/L from glucose and from 19 mmol H₂/L to 33 mmol H₂/L from xylose. Hydrogen yield efficiency (HY) of DT-1 from glucose and xylose was 1.4 mol H₂/mol glucose and 2.2 mol H₂/mol xylose, respectively. Scale up of batch fermentative hydrogen production in proto scale (20 L working volume) at regulated pH, enhanced the HY efficiency of DT-1 from 2.2 to 2.8 mol H₂/mol xylose (1.27 fold increase in HY from laboratory scale). 84% of maximum theoretical possible HY efficiency from xylose was achieved by DT-1. Acetate and ethanol were the major metabolites generated during hydrogen production.     

Effect of thiourea on the hydrogen yield in electrolysis

The effect of thiourea (TU) on H₂ evolution has been studied in 1.0 M Na₂SO₄ + x mM TU (x = 0, 5, 15, 50) at different pH (from 2–8) on Pt electrode by using electrolysis. The theoretical and experimental discharge potentials of the systems have been determined. The amounts of hydrogen gas produced at different times on the cathode at a constant potential (5 V) were measured and the hydrogen yield was calculated. From the data obtained, it reveals that the highest yield of H₂ is obtained, when 1.0 M Na₂SO₄+ 50 mM TU solution was used at pH = 8.     

Electrochemical preparation of a novel,effective and low cast catalytic surface for hydrogen evolution reaction

The formation of platinum nucleus on the freshly polished aluminum (Al) and anodized aluminum electrodes (Al₂O₃/Al) was studied by cyclic voltammetry. Results showed that the deposition of platinum on freshly polished aluminum from an aqueous 0.5 M phosphate buffer solution containing H₂PtCl₆ takes place rapidly through the electroreduction of dissolved Pt (IV) ions. At shorter deposition times, small particles of platinum crystals were formed on the aluminum and the surface coverage was imperfect. At longer deposition times, the size of the platinum crystals increases while their number decreases due to the coalescence and agglomeration processes. The electrodeposition of Pt on the Al electrode was conveniently carried out over the Al₂O₃/Al electrode. The electrochemical and catalytic activities of the Pt/Al and Pt/Al₂O₃/Al electrodes were studied in 0.1 M H₂SO₄ solution. In cyclic voltammetry, the two pair symmetric peaks appeared in 0.1 M H₂SO₄ solution which was attributed to the formation of strongly (H_s) and weakly bounded hydrogen (H_w). The occurrence of the third anodic hydrogen peak (H_3rd) was revealed at low scan rate and in high concentration of H₂SO₄. At potentials more negative than −0.3 V vs. SCE, the current is mainly due to hydrogen evolution reaction. The influence of the various parameters such as deposition method and amount of platinum, sulfuric acid concentration and medium temperature on the hydrogen evolution reaction is described. Finally the kinetic of the hydrogen evolution reaction is also discussed on the Pt/Al electrode.     

Effect of carbon coating on Cu electrodes for hydrogen production by water splitting

In recent years, fossil fuel depletion has been increasing, which leads to environmental issues. Hydrogen energy is considered a promising renewable energy to replace fossil fuels because it is a sustainable, clean, and green energy source. Among hydrogen production methods, water splitting has the highest reliability and is used the most often. Platinum is normally used as water splitting catalyst and an electrode. However, there has been much effort to replace it as such owing to its high cost. Copper (Cu) is not used as water splitting catalyst or an electrode, despite its high current density, because of its corrosive properties. In this study, carbon was coated onto a Cu substrate and a hydrogen production experiment was carried out with 0.1 M Na₂SO₄ and 0.1 M H₂SO₄ electrolytes. As a result, the carbon coating decreased oxidation rate of the Cu electrode and effected stability in short-term hydrogen evolution experiment. This indicates the possibility of carbon-Cu electrode with other catalytic materials.     

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.     

A sequential approach to uncapping of theoretical hydrogen production in a sulfate-reducing bacteria-based bio-electrochemical system

The presence of undesired methanogens with Sulfate-reducing bacteria (SRBs) is a serious challenge faced by the bioelectrochemical system (BES). In the present study, we investigate the impact of ammonia pre-treated electrodes on hydrogen production in a 600 ml anaerobic (BES) enriched with sulfate-reducing bacteria (SRBs) to inhibit the CH₄ production for achieving the theoretical H₂ production. The highest hydrogen production of 3.67 ± 0.31 M/M of glucose was recorded in the BES. The BES completely inhibited the growth of methanogens after the 7^th cycle of operation. The higher hydrogen production efficiency of BES can be justified by assuming a higher hydrogen mass transfer from the electrode surface to the biofilm. In presence of sulfate, acetate acid type of the fermentation was dominating in hydrogen production, while limitation of SO₄^2? switch over to the dominance of butyric acid type fermentative hydrogen production. Despite the sign of change in the acetate to butyric acid type metabolism, the BES system was able to uncap the theoretical hydrogen production. The notable change in vector orientation of H₂, butyric acid, and hexanoic acid inferring the significant differences in the microbial community adapted on the electrodes in the R–NH₃ and R-Cont. SEM image clearly showing ammonia-treated electrode harbour more microbial growth on the electrode surface. The ratio obtained for CH₃ and CH₂ for the R–NH₃ and R-CONT of 1.316 and 1.755 respectively by FTIR stretching vibrations showing the difference in the bacterial species adapted on the bioanodes. Cumulative hydrogen production data was computed to confirm its validity of the Gompertz model, Richard model, and Logistic model. The Richard model was found in the best-fitted models for cumulative hydrogen production.     

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.     

Bioconversion of crude glycerol from biodiesel production to hydrogen

This study evaluates the potential of bioconversion of crude glycerol, discharged from biodiesel production plant, to hydrogen (H₂) by an enriched microbial community. Microbial community was enriched from activated sludge in a medium amended with 2.5 g/L of crude glycerol. Optimal cultivation parameters for H₂ production such as initial pH, cultivation temperature and substrate concentration were investigated. H₂ yields from raw glycerol at optimal conditions (pH 6.5; 40 °C and 1 g/L raw glycerol) were 1.1 ± 0.1 mol-H₂/mol-glycerol_consumed. H₂ production was associated with acetate-butyrate type fermentation, along with ethanol as one of the end products. Kinetic experiments on H₂ production from pure and crude glycerol indicated the absence of any inhibitory effects from the impurities present in crude glycerol. The community analysis revealed that the enriched microbial consortium was dominated mainly by Clostridium species.     

Fabrication of platinum coated nanoporous gold film electrode: A nanostructured ultra low-platinum loading electrocatalyst for hydrogen evolution reaction

The electrolytic hydrogen evolution reaction (HER) on platinum coated nanoporous gold film (PtNPGF) electrode is demonstrated. The deposition of platinum occurred as a spontaneous redox process in which a copper layer, obtained by underpotential deposition, was oxidized by platinum ions, which were reduced and simultaneously deposited. The present method could provide a very low Pt-loading electrode and the results demonstrated that ultra thin Pt coating effected efficiently and behaved as the nanostructured Pt for electrocatalytic hydrogen evolution reaction. The loading of Pt was calculated as 4.2 × 10⁻³ μg cm⁻² for PtNPGF electrode. The current density at −0.4 V and −0.8 V vs. Ag/AgCl was as high as 0.66 A μg⁻¹ Pt and 3 A μg⁻¹ Pt, respectively and the j₀ was evaluated as 0.03 mA cm⁻² or 8 mA μg⁻¹ Pt. The results indicated that increasing electrode area had no catalytic effect, but the nanostructure nature of as-fabricated electrode and submonolayer deposition of copper resulted in electrocatalytic activity for PtNPGF electrode.     

In-situ and ex-situ comparison of the electrochemical oxidation of SO2 on carbon supported Pt and Au catalysts

Electrochemical characterizations are performed using thin films and commercial carbon supported platinum and gold catalysts for sulfur dioxide oxidation, the primary electrochemical oxidation reaction in the Hybrid-sulfur (HyS) thermochemical process. Electrochemical evaluation of metal thin films qualitatively confirms the higher activity of Au over Pt, AuPt, Pd, and Ir for the electrochemical oxidation of SO₂. Ex-situ testing, using rotating disk electrode (RDE), shows an earlier onset potential for Au/C at low sulfuric acid concentrations (C ≤ 3.5 M) and a higher turnover frequency than Pt/C at sulfuric acid concentrations ranging from 3.5 M to 9 M. In-situ electrolysis experiments using low catalyst loadings (0.1 mg_Au cm⁻², a factor of ≥5 lower than typical loadings) confirm that Au nanoparticles exhibit higher current densities and greater stability than Pt nanoparticles. This is consistent with the thin film screening studies, which showed higher activity with increasing gold content in AuPt thin films. This work reveals an alternative material to state-of-the-art Pt to lower the energy needs and aid the HyS cycle in reaching the target of $2/kg H₂ set forth by the Department of Energy to achieve economic feasibility of large-scale hydrogen generation.     

Statistical optimization of biohydrogen and ethanol production from crude glycerol by microbial mixed culture

Design of Experiments (DoE) was applied to improve the ability of enriched activity sludge to efficiently convert crude glycerol from biodiesel industry into hydrogen and ethanol, using a very simple synthetic medium. Based on Plackett–Burman screening design, glycerol concentration, temperature and initial pH were identified as significant variables. Box–Behnken design and Response Surface Method (RSM) were then used for optimization. The maximum hydrogen yield of 0.96 mol H₂/mol glycerol was estimated at the temperature of 37.0 °C, initial pH of 7.9 and glycerol concentration of 15.0 g/L. Maximum hydrogen production rate of 2191 mL/L/d was estimated at the temperature of 37.3 °C, initial pH of 8.0 and glycerol concentration of 15.2 g/L. Finally maximum ethanol production of 7.92 g/L was estimated at an initial pH of 8.0 and glycerol concentration of 15.0 g/L (temperature had no significant effect). These results show that it is possible to obtain both, high yield and production of hydrogen and ethanol together, using a very simple synthetic medium, without trace element- and vitamin solution, tryptone or yeast extract.     

Hydrogen generation by alcohol reforming in a tandem cell consisting of a coupled fuel cell and electrolyser

The performance of a novel electro-reformer for the production of hydrogen by electro-reforming alcohols (methanol, ethanol and glycerol) without an external electrical energy input is described. This tandem cell consists of an alcohol fuel cell coupled directly to an alcohol reformer, negating the requirement for external electricity supply and thus reducing the cost of operation and installation. The tandem cell uses a polymer electrolyte membrane (PEM) based fuel cell and electrolyser. At 80 °C, hydrogen was generated from methanol, by the tandem PEM cell, at current densities above 200 mA cm⁻², without using an external electricity supply. At this condition the electro-reformer voltage was 0.32 V at an energy input (supplied by the fuel cell component) of 0.91 kWh/Nm³; i.e. less than 20% of the theoretical value for hydrogen generation by water electrolysis (4.7 kWh/Nm³) with zero electrical energy input from any external power source. The hydrogen generation rate was 6.2 × 10⁻⁴ mol (H₂) h⁻¹. The hydrogen production rate of the tandem cell with ethanol and glycerol was approximately an order of magnitude lower, than that with methanol.