Performance of amine-modified CdS-D@ZIF-8 nanocomposites for enhanced photocatalytic H2 evolution

The exploration of an efficient photocatalyst for H₂ evolution directly from water splitting is highly desirable due to the current environmental and energy situation. The present work successfully used a solvothermal method to synthesize organic-inorganic CdS-diethylenetriamine (CdS-D) nanorods (NRs). The amine-modified CdS-D@ZIF-8 nanocomposite materials were prepared using the self-assembly method with different ZIF-8 nanocrystals (NCs) weight ratios. At λ ≥ 420 nm wavelength, the optimized CdS-D@ZIF-8 (CZ-2) nanocomposite with 5.0 wt% loading of ZIF-8 NCs showed the highest performance of 2293.9 μmol g⁻¹ h⁻¹ H₂ evolution and an apparent quantum yield (AQY) of 4.95%. The CZ-2 nanocomposite's activity was 114.69, 5.25, and 1.32 times higher than that of ZIF-8 NCs (20.0 μmol g⁻¹ h⁻¹), CdS-D NRs (436.4 μmol g⁻¹ h⁻¹) and 1.0 wt% Pt/CdS-D (1737.3 μmol g⁻¹ h⁻¹), respectively. The cyclic photostability of the prepared CZ-2 nanocomposite remained unchanged after six consecutive cycles. The UV-DRS, electrochemical measurements, and Mott-Schottky (MS) analysis were performed to explain the band edge positions for CdS-D NRs and ZIF-8 NCs. The detailed S-scheme charge transfer mechanism of the as-prepared catalysts was also studied using the density functional theory (DFT). This work provides vital information for the controllable synthesis of ZIF-8-modified S-scheme nanocomposites for solar energy utilization.     

Hydrogen production from aqueous triethanolamine solution using Eosin Y-sensitized ZnO photocatalyst doped with platinum

Photocatalytic system for hydrogen production comprising ZnO as a photocatalyst, Eosin Y photo-sensitizer, triethanolamine electron donor and platinum co-catalyst is prepared and systematically tested under visible and simulated solar light irradiation. The results of laboratory experiments show that all studied parameters, such as a solution pH, Pt/ZnO dose, triethanolamine concentration and light intensity, notably influence the rate of photocatalytic hydrogen generation. The maximum hydrogen generation rate of 6.50 μmol min⁻¹ is achieved at pH 7.0 and 2 g L⁻¹ ZnO loaded with 0.75 wt% platinum, and 0.757 M triethanolamine concentration. The rate of hydrogen production as a function of triethanolamine concentration follows Langmuir-Hinshelwood kinetic model with reaction rate constant 4.50 μmol min⁻¹ and adsorption constant 14.84 M⁻¹ in solar light and 5.26 μmol min⁻¹ and 6.67 M⁻¹ in visible light, respectively. The reaction mechanism of hydrogen generation in the tested system is proposed and discussed.     

Photoelectrocatalytic reduction of CO2 to methanol over CuFe2O4@PANI photocathode

The present study was aimed to convert CO₂ into methanol which not only addresses the potential solution for controlling the CO₂ concentration level in the atmosphere but also offers an alternative approach for the production of renewable energy source. In this perspective, a hybrid photocatalyst, PANI@CuFe₂O₄ was synthesized, characterized and used as a photocathode for photoelectrocatalytic (PEC) reduction of CO₂ to methanol in aqueous medium at an applied potential of ?0.4 V vs NHE under visible light irradiation. The combination of PANI with CuFe₂O₄ greatly increased the PEC CO₂ reduction to methanol owing to enhance the CO₂ chemisorption capacity by the photocathode surface and at the same time facilitated the separation of photogenerated electron-hole (e^?/h⁺) pairs. The incident photon to current efficiency (IPCE) and quantum efficiency (QE) for methanol formation in PEC CO₂ reduction could be achieved as 7.1 and 24.0% respectively. The rate of formation of methanol in PEC CO₂ reduction was found as 49.3 μmol g^?1h^?1 with 73% Faradaic efficiency. Compared to photocatalytic reaction, the PEC results demonstrated that the applied potential could effectively separate the photogenerated e^?/h⁺ pairs and therefore, enhanced the PEC CO₂ reduction activity of the hybrid photocatalyst.     

Two-stage photoautotrophic cultivation to improve carbohydrate production in Chlamydomonas reinhardtii

A two-stage strategy was developed to improve the microalgal carbohydrate accumulation for advanced biofuel production. In the first stage, Chlamydomonas reinhardtii CC125 was cultivated in photo-bioreactors by repeated fed batch operation to improve the biomass production. Optimal culture conditions achieved in the batch operation were applied to the repeated fed batch operation. Biomass productivity reached 0.47 g L⁻¹ d⁻¹ with 70% medium replacement ratio and 5% CO₂ under continuous light of 135 μmol m⁻² s⁻¹. In the second stage, reducing CO₂ content to 0.04% led to a high carbohydrate content of 71%, showing more than 9 times improvement compared to that in the biomass from the first stage culture. These results suggest that photoautotrophic two-stage cultivation is an effective approach to accumulate microalgal carbohydrate as a feedstock for biofuel production.     

Green synthesized carbon quantum dots as TiO2 sensitizers for photocatalytic hydrogen evolution

Carbon quantum dots (CQDs) have attracted growing interest due to their superior luminescent properties, which make them excellent photosensitizers for TiO₂. This study presents the green-synthesis of CQDs from edible mushroom Agaricus bisporus through microwave irradiation. In the study as-synthesized CQDs were used as a sensitizer for TiO₂ in photocatalytic hydrogen evolution in aqueous triethanolamine (sacrificial reagent) under visible-light irradiation. Photocatalytic hydrogen production activity of CQD-sensitized TiO₂ was found to be 472 μmol g⁻¹ h⁻¹ (without loading any noble metal co-catalyst) and 1458 μmol g⁻¹ h⁻¹ (with loading Pt co-catalyst). The study revealed that the CQDs from mushroom A. bisporus can be used as an efficient sensitizer for TiO₂ in photocatalytic hydrogen production.     

Photocatalytic hydrogen evolution assisted by aqueous (waste)biomass under simulated solar light: Oxidized g-C3N4 vs. P25 titanium dioxide

Oxidized graphitic carbon nitride (o-g-C₃N₄) and Evonik AEROXIDE^® P25 TiO₂ were compared for lab-scale photocatalytic H₂ evolution from aqueous sacrificial biomass-derivatives, under simulated solar light. Experiments in aqueous starch using Pt or Cu–Ni as the co-catalysts indicated that H₂ production is affected by co-catalyst type and loading, with the greatest hydrogen evolution rates (HER) up to 453 and 806 μmol g⁻¹ h⁻¹ using TiO₂ coupled with 3 wt% Cu–Ni or 0.5 wt% Pt, respectively. Despite the lower surface area, o-g-C₃N₄ gave HERs up to 168 and 593 μmol g⁻¹ h⁻¹ coupled with 3 wt% Cu–Ni or 3 wt% Pt. From mono- and di-saccharide solutions, H₂ evolution was in the range 504–1170 μmol g⁻¹ h⁻¹ for Pt/TiO₂ and 339–912 μmol g⁻¹ h⁻¹ for Cu–Ni/TiO₂, respectively; o-g-C₃N₄ was efficient as well, providing HERs of 90–610 μmol g⁻¹ h⁻¹. The semiconductors were tested in sugar-rich wastewaters obtaining HERs up to 286 μmol g⁻¹ h⁻¹. Although HERs were lower compared to Pt/TiO₂, a cheap, eco-friendly and non-nanometric catalyst such as o-g-C₃N₄, coupled to non-noble metals, provided a more sustainable H₂ evolution.     

Preparation and characterization of Sm0.2Ce0.8O1.9/Na2CO3 nanocomposite electrolyte for low-temperature solid oxide fuel cells

Sm_0.2Ce_0.8O_1.9 (SDC)/Na₂CO₃ nanocomposite synthesized by the co-precipitation process has been investigated for the potential electrolyte application in low-temperature solid oxide fuel cells (SOFCs). The conduction mechanism of the SDC/Na₂CO₃ nanocomposite has been studied. The performance of 20 mW cm⁻² at 490 °C for fuel cell using Na₂CO₃ as electrolyte has been obtained and the proton conduction mechanism has been proposed. This communication demonstrates the feasibility of direct utilization of methanol in low-temperature SOFCs with the SDC/Na₂CO₃ nanocomposite electrolyte. A fairly high peak power density of 512 mW cm⁻² at 550 °C for fuel cell fueled by methanol has been achieved. Thermodynamical equilibrium composition for the mixture of steam/methanol has been calculated, and no presence of C is predicted over the entire temperature range. The long-term stability test of open circuit voltage (OCV) indicates the SDC/Na₂CO₃ nanocomposite electrolyte can keep stable and no visual carbon deposition has been observed over the anode surface.     

Effect of carbon supply mode on biomass and lipid in CSMCRI's Chlorella variabilis (ATCC 12198)

CSIR-CSMCRI's Chlorella variabilis (ATCC 12198) was evaluated through autotrophic, mixotrophic and heterotrophic growth for lipid production. Autotrophic growth was assessed by providing sodium bicarbonate/sodium carbonate/CO₂ (air in a medium). Higher lipid productivity (115.94 mg L⁻¹ d⁻¹) with higher biomass productivity (724.98 mg L⁻¹ d⁻¹) of this strain was attained through bicarbonate and CO₂ sequestration in a photobioreactor. Ability to regulate the pH in favorable bicarbonate/carbonate ratio showed its potential in alkaline effluent based carbon sequestration system for biofuel generation. The simultaneous study was also conducted to understand the effect of elevated CO₂ (0.4, 1 and 1.2 g L⁻¹) in air on the culture to assess adaptation, growth and lipid in the closed chamber conditions. It was observed that CO₂ sequestration by the microalgae from the CO₂ enriched environment was optimum at 1 g L⁻¹ C. variabilis adapted to comparatively higher CO₂ (1 g L⁻¹) but grew better in low CO₂ (0.4 g L⁻¹). It was also observed that the growth, lipid content and fatty acid composition was significantly affected by CO₂ supply strategies. The effect of intermittently added sodium bicarbonate at different pH on microalgal lipid content and composition of fatty acids was observed which could affect the quality of biodiesel. The effect on fatty acid composition was observed in response to carbon supply mode during the microalgal growth at different pH dictating the properties of biodiesel.     

Dehydrogenation of pure methanol in an alkaline solution using copper electrodes

Herein, we focused on electrolysis to produce hydrogen-based energy to reduce pollution and cost of energy generation by replacing platinum (Pt) and ruthenium (Ru) anodes with copper (Cu) anodes, while demonstrating that H₂ and CO can be obtained by dehydrogenating pure methanol in a non-compartment cell. Also this is a new study that is completely different from DMFC. Redox products of methanol and electrochemical efficiency were determined using various techniques. 1 V (vs Ag/AgCl [KCl sat’]) was applied to quantitatively evaluate H₂ generation; on average, 801.17 mmol g⁻¹ L⁻¹ h⁻¹ of H₂ was generated. The Cu electrode was electrochemically stable under the stirring at 150 rpm, indicating reduced toxicity by CO adsorption. Gas-phase CO and H₂, along with liquid-phase formate, carbonate, and paraformaldehyde, were obtained; the main product was H₂. However, details of the dehydrogenation mechanism remain unclear, and merit further investigations.     

Preparation and study of electrocatalytic activity of Ni-Pd(OH)2/C nanocomposite for hydrogen evolution reaction in alkaline solution

A new catalyst (Ni-Pd(OH)₂/C) for hydrogen evolution reaction (HER) was prepared by coelectrodeposition of Pd(OH)₂/C nanoparticles and Ni on a Cu substrate in two steps. Furthermore, the effect of Mo ions in alkaline solution (1 M NaOH) on the electrocatalytic activity of Ni-Pd(OH)₂/C nanocomposite was studied as an in-situ activator for the HER. The various electrochemical methods were employed to study the HER activity of the investigated new catalyst, including linear sweep voltammetry (LSV), the steady-state polarization Tafel curves, electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The electrochemical measurements showed that the Ni-Pd(OH)₂/C nanocomposite as a catalyst for the HER has an excellent catalytic activity with good stability in alkaline solution. Furthermore, the rate constants of the forward and backward reactions of Volmer and Heyrovský steps were estimated using Tafel-impedance data and revealed that the proton discharge electrosorption or Volmer reaction (k₁= (6.8 ± 0.7) × 10⁻⁸ mol cm⁻² s⁻¹) was the rate determining step (RDS) of the HER on the surface of Ni-Pd(OH)₂/C nanocomposite. Also, it was observed that the presence of Mo ions in alkaline solution could significantly increase the HER activity of Ni-Pd(OH)₂/C nanocomposite. The comparison of RDS rate constant value with surface roughness (R_f) of Ni-Pd(OH)₂/C catalyst showed that its high activity toward the HER originated from both increase in the surface roughness (∼20%) and increase in synergistic effect (∼80%).     

Comparative study of the effect of TiO2 support composition and Pt loading on the performance of Pt/TiO2 photocatalysts for catalytic photoreforming of cellulose

Herein, catalytic aqueous phase photoreforming of cellulose was carried out over Pt/m-TiO₂ (i.e., mixed phase of anatase and rutile) and Pt/anatase catalysts to investigate the effect of the TiO₂ support structure and Pt loading on the production of H₂. The effect of the TiO₂ support on the properties of the resulting Pt/TiO₂ catalysts (such as actual Pt loading and BET surface area) was not significant. At low Pt loading of 0.16 wt.%, the TiO₂ supports affected the sub-nanometre Pt structures which was confirmed by the diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterisation (using CO as the probe). Conversely, the effect of TiO₂ supports on larger Pt particles (on 1 wt.% catalysts) was insignificant possibly due to the reduced effect of restructuration of bigger Pt particles on the TiO₂ supports. With an increase in Pt loading from 0.16 wt% to 1.00 wt.%, the normalised H₂ production rate (with respect to the actual supported Pt amount and specific surface area of the catalysts) showed a decreasing trend over the two types of the catalysts, i.e., from 10.6 to 1.4 μmol h⁻¹ m⁻² mg_Pt⁻¹ for Pt/m-TiO₂, and from 8.5 to 1.2 μmol h⁻¹ m⁻² mg_Pt⁻¹ for Pt/anatase. Specifically, large Pt particle sizes reduced the CO₂/H₂ production from cellulose photoreforming over both Pt/m-TiO₂ and Pt/anatase catalysts, indicting an important role played by Pt particle size in photoreforming. Interestingly, in this study, the m-TiO₂ supported catalysts only showed the benefits of enhanced charge separation across the phase junction in producing H₂ with small Pt particles (at sub-nanometre), whilst, when large Pt particles (at around 1–2 nm) were supported, such a benefit was not significant in cellulose photoreforming. The promoting effect of small, sub-nm particles is attributed to the better capture of photoelectrons from bulk TiO₂ and better activity of H⁺ coupling on small Pt particle. Further fundamental study on such guest-host interactions is devised to optimise Pt/TiO₂ catalysts for improving H₂ production from photoreforming reactions.     

Single-phase Ni3Sn alloy alkali-leached for hydrogen production from methanol decomposition

Methanol decomposition over alkali-leached Ni₃Sn powder at 513–793 K was investigated. Compared with untreated Ni₃Sn, alkali-leached Ni₃Sn had high catalytic activity and selectivity toward H₂ and CO production above 633 K. A maximum H₂ production rate of 100 × 10⁻³ mol h⁻¹ g-Cat⁻¹ and H₂ selectivity above 95% were attained over alkali-leached Ni₃Sn at 793 K. Alkali-leached Ni₃Sn presented good catalytic activity for 45 h of reaction at 713 K, whereas Ni₃Sn had none. The activation energy was calculated, and its values rapidly decreased from Ni₃Sn to alkali-leached ones. The improvement was attributed to the formation of Ni nanoparticles less than 100 nm in diameter in the alkali-leaching process, which had high activity for methanol decomposition. The improved catalytic activity favored the gradual formation of fine Ni₃Sn particle during the reaction, which served as the active sites for methanol decomposition when the catalytic activity decreased because of carbon deposition on the Ni surface. Results demonstrated that alkali-leached Ni₃Sn was a promising potential catalyst for hydrogen production from methanol.     

Zinc oxide functionalized molybdenum disulfide heterostructures as efficient electrocatalysts for hydrogen evolution reaction

Technology urges to replace the state-of-the-art catalysts such as platinum with low cost, earth abundant and durable electrocatalysts for efficient hydrogen evolution (HER) reaction which is going to become the major sustainable production of energy in future. Herein, we present the heterostructure based MoS₂.ZnO (MZO) heterostructures for successful electrochemical water splitting process. For HER, the prepared MoS₂.ZnO nanocomposites show the over potential as low as 239 mV at cathodic current density 10 mAcm⁻² with an exchange current density of 3.2 μAcm⁻². A Tafel slope of about 62 mV per decade suggested to have the Volmer-Heyrovsky mechanism for the HER process with MoS₂.ZnO nanocomposite as the catalyst. The small Tafel slope indicates a promising electrocatalyst for HER in practical application. The strong interface formation at the MoS₂.ZnO heterostructure facilitates higher catalytic activity and excellent cycling stability. The heterostructure formation based on semiconductor two dimensional (2D) transition metal dichalcogenides (TMDC) open up new avenues for effective manipulation of HER catalysts.     

Application of experimental design methodology for optimization of biofuel production from microalgae

Optimization of biofuel productivity, in terms of lipid content, polysaccharide content, and calorific value, from microalgae was performed by varying four variables (temperature, light intensity, nitrogen content, and CO₂ addition) using a 2⁴ full factorial design. A statistical analysis showing the influence of each variable and their interactions was conducted. The selected variables all influence biofuel productivity, but their importance varies according to the sequence: CO₂ addition > temperature > nitrogen content > light intensity. Interactive effects of temperature with light intensity and nitrogen with CO₂ addition for lipid and polysaccharide productivities were identified, respectively. For calorific value, interactive effects of CO₂ addition with light intensity and nitrogen content were observed. The highest biofuel productivity was obtained at the following conditions: temperature (>25 °C), light intensity (>60 μmol photons m⁻² s⁻¹), nitrogen content (<50 mg L⁻¹), and CO₂ addition (>18 mL L⁻¹ d⁻¹). 10 days was found to be the most favorable cultivation time for lipid production under the investigated conditions.     

Screening and optimisation of hydrogen production by newly isolated nitrogen-fixing cyanobacterial strains

Recently, there has been a propensity to postpone dealing with the world's climate concerns until later, resulting in a 1.5 °C rise in temperature over the last century. Therefore, interest in biologically derived, inexhaustible energy sources based on solar energy is growing. Cyanobacteria have the potential to produce clean, renewable fuels in the form of hydrogen (H₂) gas, derived from solar energy and water. The current study reports the screening 11 cyanobacterial strains isolated from rice paddies and hotsprings for efficient H₂ producers. According to our findings, H₂ concentrations in the species ranged from 3.6 to 48.9 μmol mg⁻¹ Chl a h⁻¹. H₂ production by isolated species was shown to have a 2% positive influence on oxygen (O₂) and carbon dioxide (CO₂) concentrations and a 2% negative effect on all nitrogen gas (N₂) concentrations. It was discovered that at high CO₂ concentrations, photosynthesis is enhanced but H₂ production is suppressed. Anabaena variabilis BTA-1047 was found to be the most active H₂-producing species, with an H₂ production activity of 21.3 μmol mg⁻¹ Chl a h⁻¹. Moreover, a 1% O₂: 2% CO₂ gas mixture doubled the strain activity of H₂ production. The findings of the study called into the question the notion that only an anaerobic environment is required for H₂ production by N₂-fixing cyanobacterial species and explored whether H₂ productivity can be increased by stimulating the micro-anaerobic environment with a carbon source.     

Enhanced electrochemical and hydrogen storage properties of La–Mg–Ni-based alloy electrode using a Ni and N co-doped reduced graphene oxide nanocomposite as a catalyst

To enhance the electrochemical property of a La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy, a three-dimensional (3D) reduced graphene oxide (rGO)-supported nickel and nitrogen co-doped (Ni–N@rGO) nanocomposite is fabricated by an impregnation method and introduced into the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy. The results show that the reversible hydrogen storage property and the comprehensive electrochemical performance of the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy are enhanced effectively when it is modified by the Ni–N@rGO nanocomposite. The high-rate dischargeability values at a discharge current density of 1500 mA g⁻¹ for the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy and Ni–N@rGO-modified samples are 0.0% and 70.5%, respectively. Additionally, the anodic peak currents for the unmodified alloy electrode is 892 mA g⁻¹. Under the catalytic action of the Ni–N@rGO nanocomposite, the value increases to 2307 mA g⁻¹, which is 2.59 times larger than that of unmodified samples. The results also indicate that the diffusion ability of the hydrogen atom in the alloy electrode body enhances significantly when modified by the Ni–N@rGO nanocomposite. The hydrogen diffusion coefficient for the La_0.7Mg_0.3(Ni_0.9Co_0.1)_3.5 alloy electrode increases from 3.93 × 10⁻¹⁰ cm² s⁻¹ to 6.15 × 10⁻¹⁰ cm² s⁻¹ when is modified by Ni–N@rGO nanocomposite. These improvements in the comprehensive electrochemical properties are mainly attributed to the excellent electrochemical activity and conductivity of the Ni–N@rGO nanocomposite.     

A pH-differential dual-electrolyte microfluidic electrochemical cells for CO2 utilization

CO₂ can be converted to useful fuels by electrochemical processes. As an effective strategy to address greenhouse effect and energy storage shortage, electrochemical reduction of CO₂ still needs major improvements on its efficiency and reactivity. Microfluidics provides the possibility to enhance the electrochemical performance, but few studies have focused on the virtual interface. This work demonstrates a dual electrolyte microfluidic reactor (DEMR) that improves the thermodynamic property and raises the electrochemical performance based on a laminar flow membrane-less architecture. Freed from hindrances of a membrane structure and thermodynamic limitations, DEMR could bring in 6 times higher reactivity and draws electrode potentials closer to the equilibrium status (corresponded to less electrode overpotentials). The cathode potential was reduced from −2.1 V to −0.82 V and the anode potential dropped from 1.7 V to 1 V. During the conversion of CO₂, the peak Faradaic and energetic efficiencies were recorded as high as 95.6% at 143 mA/cm² and 48.5% at 62 mA/cm², respectively, and hence, facilitating future potential for larger-scale applications.     

Highly conductive proton-conducting electrolyte with a low sintering temperature for electrochemical ammonia synthesis

BaCe_0·7Zr_0.1Gd_0.2O_3-δ (BCZG) powder is synthesized by a citrate sol-gel method, and different amounts of Li₂CO₃ are introduced to lower the sintering temperature. The densification temperature of BCZG ceramic is decreased drastically to 1250 °C by using Li₂CO₃ as sintering aid. BCZG with 2.5 wt% of Li₂CO₃ (BCZG-2.5L) can not only remarkably promote the sintering process of BCZG but also enhance its electrical conductivity. The total ionic conductivity of BCZG-2.5L attains to 1.9 × 10⁻² S cm⁻¹ at 600 °C in a wet H₂ atmosphere. Ammonia synthesis at atmospheric pressure is conducted on (2K, 10Fe)/Ni-BCZG | BCZG-2.5L | Ni-BCZG electrolytic cell with an applied voltage of 0.2–1.6 V at a temperature of 450–600 °C. The highest NH₃ formation rate of 1.87 × 10⁻¹⁰ mol s⁻¹ cm⁻² and the highest current efficiency of 0.53% is achieved at 500 °C with an applied voltage of 0.8 V.     

Supercritical water gasification of timothy grass as an energy crop in the presence of alkali carbonate and hydroxide catalysts

This study is focused on identifying the candidature of timothy grass as an energy crop for hydrogen-rich syngas production through supercritical water gasification. Timothy grass was gasified in supercritical water to investigate the impacts of temperature (450–650 °C), biomass-to-water ratio (1:4 and 1:8) and reaction time (15–45 min) in the pressure range of 23–25 MPa. The impacts of carbonate catalysts (e.g., Na₂CO₃ and K₂CO₃) and hydroxide catalysts (e.g., NaOH and KOH) at variable mass fractions (1–3%) were examined to maximize hydrogen yields. In the non-catalytic gasification of timothy grass, highest hydrogen (5.15 mol kg⁻¹) and total gas yields (17.2 mol kg⁻¹) with greater carbon gasification efficiency (33%) and lower heating value (2.21 MJ m⁻³) of the gas products were obtained at 650 °C with 1:8 biomass-to-water ratio for 45 min. However, KOH at 3% mass fraction maximized hydrogen and total gas yields up to 8.91 and 30.6 mol kg⁻¹, respectively. Nevertheless, NaOH demonstrated highest carbon gasification efficiency (61.3%) and enhanced lower heating value of the gas products (4.68 MJ m⁻³). Timothy grass biochars were characterized through Fourier transform infrared spectroscopy, Raman spectroscopy and scanning electron microscopy to understand the behavior of the feedstock to rising temperature and reaction time. The overall findings suggest that timothy grass is a promising feedstock for hydrogen production via supercritical water gasification.     

Electrochemical impedance studies of electrooxidation of methanol and formic acid on Pt/C catalyst in acid medium

Cyclic voltammetry (CV), amperometric i − t experiments, and electrochemical impedance spectroscopy (EIS) measurements were carried out by using glassy carbon disk electrode covered with the Pt/C catalyst powder in solutions of 0.5 mol L⁻¹ H₂SO₄ containing 0.5 mol L⁻¹ CH₃OH and 0.5 mol L⁻¹ H₂SO₄ containing 0.5 mol L⁻¹ HCOOH at 25 °C, respectively. Electrochemical measurements show that the activity of Pt/C for formic acid electrooxidation is prominently higher than for methanol electrooxidation. EIS information also discloses that the electrooxidation of methanol and formic acid on the Pt/C catalyst at various polarization potentials show different impedance behaviors. The mechanisms and the rate-determining steps of formic acid electrooxidation are also changed with the increase of the potential. Simultaneously, the effects of the electrode potentials on the impedance patterns were revealed.