Robust hydrogen detection system with a thermoelectric hydrogen sensor for hydrogen station application

A prototype hydrogen detection system using the micro-thermoelectric hydrogen sensor (micro-THS) was developed for the safety of hydrogen infrastructure systems, such as hydrogen stations. We have designed a detection part with a pressure proof enclosure adoptable for the international standard of Exd II CT3, and carried out an explosion strength test, explosion and fire hazard tests, and an impact test. The hydrogen sensing performance of the detection part of this prototype system showed a good linear relationship between the sensing signal and hydrogen concentrations in air, for a wide range of hydrogen concentrations from 10 ppm to 40,000 ppm (4 vol.%). This prototype detection system was installed in the outdoor field of the hydrogen station and the response for H₂ gas in air of 100 ppm, 1000 ppm, and 10000 ppm was tested monthly for 1 year.     

Hydrogen gas sensing based on polyaniline/anatase titania nanocomposite

Polyaniline (emeraldine)/anatase TiO₂ nanocomposite (PA-NC) was prepared by a chemical oxidative polymerization. The thin films of PA-NC for hydrogen gas sensing application were deposited on Cu-interdigited electrodes by spin coating technique. A study on characteristics of PA-NC thin films was demonstrated by a porous cylindrical morphology. The response and response/recovery time of sensors for hydrogen gas were evaluated by the change of TiO₂ wt% at environmental conditions. Resistance-sensing measurement was exhibited a high sensitivity about 1.63, a good Long-term response, low response time and recovery time about 83 s and 130 s, respectively, at 0.8 vol% hydrogen gas for PA-NC including 25% wt of anatase nanoparticles. The current–voltage characteristics of PA-NC gas sensors before and after hydrogen gas injection showed a nonlinear ohmic current. Moreover, we studied the formation of PA-NCs and their hydrogen gas sensing mechanism based on contact regions in PA-NC.     

Hydrogen gas sensor based on mesoporous In2O3 with fast response/recovery and ppb level detection limit

Hydrogen gas sensors were fabricated using mesoporous In₂O₃ synthesized using hydrothermal reaction and calcination processes. Their best performance for the hydrogen detection was found at a working temperature of 260 °C with a high response of 18.0 toward 500 ppm hydrogen, fast response/recovery times (e.g. 1.7 s/1.5 s for 500 ppm hydrogen), and a low detection limit down to 10 ppb. Using air as the carrier gas, the mesoporous In₂O₃ sensors exhibited good reversibility and repeatability towards hydrogen gas. They also showed a good selectivity for hydrogen compared to other commonly investigated gases including NH₃, CO, ethyl alcohol, ethyl acetate, styrene, CH₂Cl₂ and formaldehyde. In addition, the sensors showed good long-term stability. The good sensing performance of these hydrogen sensors is attributed to the formation of mesoporous structures, large specific surface areas and numerous chemisorbed oxygen ions on the surfaces of the mesoporous In₂O₃.     

Aerogel sheet of carbon nanotubes decorated with palladium nanoparticles for hydrogen gas sensing

In the development of hydrogen sensors, it is required to meet the demands of both high sensor performance as well as the ease of fabrication for mass production. For this purpose we proposed a chemiresistive hydrogen sensors based on an aerogel sheet of carbon nanotubes decorated with palladium nanoparticles (CNT/Pd sheet). The fabrication process is straightforward that a dry-spun CNT aerogel sheet is suspended between concentric electrodes followed by depositing Pd nanoparticles on CNT sheets by thermal evaporation. The present CNT/Pd sheet sensors can detect hydrogen at concentrations as low as 2 ppm at room temperature with a detection range from 2 to 1000 ppm. The aerogel nature of CNT/Pd sheet contributes to low detection limit and broad detection range of the CNT/Pd sensor. Relations between hydrogen concentration and sensor response and response time, and the effects of temperature on sensor performance were investigated.     

Highly sensitive hydrogen sensor based on a new suspended structure of cross-stacked multiwall carbon nanotube sheet

In this research, we proposed a highly sensitive hydrogen sensor based on a new suspended structure of cross-stacked multiwall carbon nanotube (MWCNT) sheet. MWCNT sheet is a kind of CNT film which has a super-high CNT alignment and can be easily prepared by drawing from the spinnable CNT array in large scales. By stacking the sheets onto an electrode with a 1 × 1 cm hole in mutually perpendicular directions, sensors with suspended cross-stacked structure were realized. Afterwards, a two-side Pd functionalization was introduced. The effects of suspended structure, cross-stacked structure and two-side Pd functionalization were investigated respectively. It was observed that the sample with 2 + 1 layers of cross-stacked MWCNT sheet and two-side 3 nm Pd deposition showed the best gas sensing performance with a relative resistance change of 35.30% at 4% H₂. This result indicates that the proposed sensor is one of the best among all reported MWCNT based hydrogen sensors. The method demonstrated in this research gives a potential solution for the mass production of CNT-based sensors with high sensitivity and reliability.     

Extending the detection range and response of TiO2 based hydrogen sensors by surface defect engineering

With the increasing usage of hydrogen energy, the requirements for hydrogen detection technology is increasingly crucial. In addition to bringing down the working temperature, further improvement in the response and broadening the detection range of hydrogen sensors in particular are still needed. TiO₂ based sensors show great promise due to their stable physical and chemical properties as well as low cost and easy fabrication, but their detection range and low concentration response requires further improvement for practical applications. Here (002) oriented rutile TiO₂ thin films are prepared by a hydrothermal method followed by annealing in either air, oxygen, vacuum or H₂ and the hydrogen sensing performance are evaluated. Raman results show that TiO₂ thin films annealed in vacuum and hydrogen have more oxygen vacancies, while those annealed in air and oxygen have a more stoichiometric surface. Annealing in an oxygen-rich atmosphere is shown to extend the detection range of the TiO₂ sensors while annealing in anaerobic atmospheres increases their response. At high hydrogen concentrations surface adsorbed O₂⁻ is the dominant factor, while at low concentrations the Schottky barrier between Pt and TiO₂ is key to achieving a high response. Here we show controlling the TiO₂ surface properties is essential for optimizing hydrogen detection over specific concentration ranges. We demonstrate that adjusting the annealing conditions and ambient provides a simple method for tuning the performance of room temperature operating TiO₂ based hydrogen sensors.     

Construction of ternary hybrid layered reduced graphene oxide supported g-C3N4-TiO2 nanocomposite and its photocatalytic hydrogen production activity

Reduced graphene oxide (rGO) supported g-C₃N₄-TiO₂ ternary hybrid layered photocatalyst was prepared via ultrasound assisted simple wet impregnation method with different mass ratios of g-C₃N₄ to TiO₂. The synthesized composite was investigated by various characterization techniques, such as XRD, FTIR, Raman Spectra, FE-SEM, HR-TEM, UV vis DRS Spectra, XPS Spectra and PL Spectra. The optical band gap of g-C₃N₄-TiO₂/rGO nanocomposite was found to be red shifted to 2.56 eV from 2.70 eV for bare g-C₃N₄. It was found that g-C₃N₄ and TiO₂ in a mass ratio of 70:30 in the g-C₃N₄-TiO₂/rGO nanocomposite, exhibits the highest hydrogen production activity of 23,143 μmol g^?1h^?1 through photocatalytic water splitting. The observed hydrogen production rate from glycerol-water mixture using g-C₃N₄-TiO₂/rGO was found to be 78 and 2.5 times higher than g-C₃N₄ (296 μmol g^?1 h^?1) and TiO₂ (11,954 μmol g^?1 h^?1), respectively. A direct contact between TiO₂ and rGO in the g-C₃N₄-TiO₂/rGO nanocomposite produces an additional 10,500 μmol g^?1h^?1 of hydrogen in 4 h of photocatalytic reaction than the direct contact between g-C₃N₄ and rGO. The enhanced photocatalytic hydrogen production activity of the resultant nanocomposite can be ascribed to the increased visible light absorption and an effective separation of photogenerated electron-hole pairs at the interface of g-C₃N₄-TiO₂/rGO nanocomposite. The effective separation and transportation of photogenerated charge carriers in the presence of rGO sheet was further confirmed by a significant quenching of photoluminescence intensity of the g-C₃N₄-TiO₂/rGO nanocomposite. The photocatalytic hydrogen production rate reported in this work is significantly higher than the previously reported work on g-C₃N₄ and TiO₂ based photocatalysts.     

Tungsten-molybdenum oxide nanowires/reduced graphene oxide nanocomposite with enhanced and durable performance for electrocatalytic hydrogen evolution reaction

Hydrogen has attracted huge interest globally as a durable, environmentally safe and renewable fuel. Electrocatalytic hydrogen evolution reaction (HER) is one of the most promising methods for large scale hydrogen production, but the high cost of Pt-based materials which exhibit the highest activity for HER forced researchers to find alternative electro-catalyst. In this study, we report noble metal free a 3D hybrid composite of tungsten-molybdenum oxide and reduced graphene oxide (GO) prepared by a simple one step hydrothermal method for HER. Benefitting from the synergistic effect between tungsten-molybdenum oxide nanowires and reduced graphene oxide, the obtained W-Mo-O/rGO nanocomposite showed excellent electro-catalytic activity for HER with onset potential 50 mV, a Tafel slope of 46 mV decade^?1 and a large cathodic current, while the tungsten-molybdenum oxide nanowires itself is not as efficient HER catalyst. Additionally, W-Mo-O/rGO composite also demonstrated good durability up to 2000 cycles in acidic medium. The enhanced and durable hydrogen evolution reaction activity stemmed from the synergistic effect broadens noble metal free catalysts for HER and provides an insight into the design and synthesis of low-cost and environment friendly catalysts in electrochemical hydrogen production.     

The use of on-line hydrogen sensor for studying inert gas effects and nitrogen crossover in PEMFC system

The design and construction of a polymer electrolyte membrane fuel cell (PEMFC) system test bench suitable for investigating the effects of inert gas build-up and hydrogen quality on the performance of PEMFC systems is reported. Moreover, a new methodology to measure the inert gas crossover rate using an on-line hydrogen concentration sensor is introduced, and preliminary results are presented for an aged 8 kW PEMFC stack. The system test bench was also characterized using the same stack, whereupon its performance was observed to be close to commercial systems. The effect of inert gas accumulation and hence the quality of hydrogen on the performance of the system was studied by diluting hydrogen gas in the anode supply pipeline with nitrogen. During these experiments, uneven performance between cells was observed for the aged stack.     

Combustion performances of premixed ammonia/hydrogen/air laminar and swirling flames for a wide range of equivalence ratios

Ammonia, a carbon-free source of hydrogen has recently gained considerable attention as energy solution towards a green future. Previous works have shown that adding 30_VOL.% hydrogen with ammonia can eradicate the drawbacks of pure ammonia combustion but no study in the literature has investigated this blend across a wide range of equivalence ratios. The present work investigates 70/30_VOL.% NH₃/H₂ blend from 0.55 ≤ Φ ≤ 1.4 for both premixed laminar spherically expanding flames and turbulent swirling flames at atmospheric conditions. A detailed chemistry analysis has been conducted in Ansys CHEMKIN-PRO platform using a chemical reactor network (CRN) model to simulate the swirling turbulent flames. NO and NO₂ emissions have followed similar bell-shaped trends, peaking at around Φ = 0.8, while N₂O emission rises at lean conditions (Φ ≤ 0.7). The results indicate that Φ = 1.2 is the optimum equivalence ratio with reduced NO_X emissions and some ammonia slip.     

Preparation and characterization of tantalum/polyaniline composite based chemiresistor type sensor for hydrogen gas sensing application

In the present work we have reported the effect of Shift heavy ion (SHI) irradiation on the gas sensing properties of tantalum (Ta)/Polyaniline (PANI) composite thin film based chemiresistor type gas sensor for hydrogen gas sensing application. PANI was synthesized chemically by in situ oxidative polymerization method. The thin sensing films of PANI were deposited onto finger type Cu-interdigited electrodes using spin cast technique and a thin Ta layer was deposited on to PANI thin film to prepare Ta/PANI composite chemiresistor sensor. These chemiresistor sensing films were irradiated with energetic Au⁺¹² ions (150 MeV) at the different fluencies ranging from 1 × 10⁹ to 1 × 10¹¹ ions/cm². The structural and morphological properties of these composite thin films were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements before and after SHI irradiation. The electrical properties of these composite thin films were characterized by I–V characteristic measurements. The changes in resistance of the composite thin film sensor were utilized for detection of hydrogen gas. It was observed that after SHI irradiation Ta/PANI composite sensor shows a high response value and sensitivity with good repeatability in comparison to the pristine sample.     

Nanocomposite of BiPO4 and reduced graphene oxide as an efficient photocatalyst for hydrogen evolution

Nanocomposites of BiPO₄ and reduced graphene oxide (BiPO₄/RGO) synthesized by hydrothermal method, hydrazine reduction, and UV-assisted photoreduction method were studied as photocatalysts for hydrogen evolution from ethanol aqueous solution under irradiation. The incorporation of RGO into BiPO₄ significantly enhanced the photocatalytic activity for H₂ evolution, and the photocatalytic activity increases in the order of BiPO₄/RGO-hydrothermal > BiPO₄/RGO-photoreduction > BiPO₄/RGO-hydrazine. The optimum proportion of GO is 2 wt% for all the samples prepared by different methods. The rate of H₂ production calculated for BiPO₄/RGO-hydrothermal (with 2 wt% GO) nanocomposite was about 306 μmol/h/g, which was almost 2 times as high as that for bare BiPO_4. The XRD, Raman and XPS characterization suggested that the original GO was successfully reduced to RGO. The more intimate contact between BiPO₄ and RGO, the higher photocurrent responses and the higher reduction degree of RGO was consistent with the higher photocatalytic performance.     

Synthesis and characterization of porous HKUST-1 metal organic frameworks for hydrogen storage

Hydrogen storage capacity has been investigated on a copper-based metal organic framework named HKUST-1 with fine structural analyses. The crystalline structure of HKUST-1 MOF has been confirmed from the powder X-ray diffraction and the average particle diameter has been found about 15–20 μm identified by FE-SEM. Nitrogen adsorption isotherms show that HKUST-1 MOF has approximately type-I isotherm with a BET specific surface area of 1055 m²g⁻¹. Hydrogen adsorption study shows that this material can store 0.47 wt.% of H₂ at 303 K and 35 bar. The existence of Cu (II) in crystalline framework of HKUST-1 MOF has been confirmed by pre-edge XANES spectra. The sharp feature at 8985.8 eV in XANES spectra represents the dipole-allowed electron transition from 1s to 4p_xy. In addition, EXAFS spectra indicate that HKUST-1 MOF structure has the Cu–O bond distance of 1.95 Å with a coordination number of 4.2.     

Comparison of magnetite/reduced graphene oxide nanocomposites and magnetite nanoparticles on enhancing hydrogen production in dark fermentation

Magnetite/reduced graphene oxide nanocomposites (Fe₃O₄-rGO NCs) and magnetite nanoparticles (Fe₃O₄ NPs) were added to enhance biohydrogen (bioH₂) production in dark fermentation. Concentration of supplements from 10 to 100 mg/L was appropriate to enhance bioH₂ production, and inhibition appeared once concentration exceeded 100 mg/L. The best bioH₂ yield was 198.30 mL/g glucose at 100 mg/L Fe₃O₄ NPs and 225.60 mL/g glucose at 100 mg/L Fe₃O₄-rGO NCs, which was 42.97% and 62.65% higher than that in the blank group, respectively. Both Fe₃O₄ NPs and Fe₃O₄-rGO NCs could intensify butyrate-type fermentation and change the hydrogen-producing microorganism cells morphology, but the enhancement effect of Fe₃O₄-rGO NCs was superior. Microbial community structure analysis showed that Clostridium-sensu-stricto-1 became more dominant ultimately by Fe₃O₄-rGO NCs.     

Stabilized zirconia-based sensor utilizing SnO2-based sensing electrode with an integrated Cr2O3 catalyst layer for sensitive and selective detection of hydrogen

A highly selective hydrogen (H₂) sensor has been successfully developed by using an yttria-stabilized zirconia (YSZ)-based mixed-potential-type sensor utilizing SnO₂ (+30 wt.% YSZ) sensing electrode (SE) with an intermediate Al₂O₃ barrier layer which was coated with a catalyst layer of Cr₂O₃. The sensor utilizing SnO₂ (+30 wt.% YSZ)-SE was found to be capable of detecting H₂ and propene (C₃H₆) sensitively at 550 °C. In order to enhance the selectivity towards H₂, a selective C₃H₆ oxidation catalyst was employed to minimize unwanted responses caused by interfering gases. Among the examined metal oxides, Cr₂O₃ facilitated the selective oxidation of C₃H₆. However, the addition or lamination of Cr₂O₃ to SnO₂ (+30 wt.% YSZ)-SE was found to diminish the sensing responses to all examined gases. Therefore, an intermediate layer of Al₂O₃ was sandwiched between the SE layer and the catalyst layer to prevent the penetration of Cr₂O₃ particles into the SE layer. The sensor using SnO₂ (+30 wt.% YSZ)-SE coated with a catalyst layer of Cr₂O₃ as well as an intermediate layer of Al₂O₃ exhibited a sensitive response toward H₂, with only minor responses toward other examined gases at 550 °C under humid conditions (21 vol.% O₂ and 1.35 vol.% H₂O in N₂ balance). A linear relationship was observed between sensitivity and H₂ concentration in the range of 20–800 ppm on a logarithmic scale. The results of sensing performance evaluation and polarization curve measurements indicate that the sensing mechanism is based on the mixed-potential model.     

Microwave-assisted one-pot hydrothermal synthesis of V and La co-doped ZnO/CNTs nanocomposite for boosted photocatalytic hydrogen production

In this work, vanadium and lanthanum co-doped ZnO/CNTs (VL-ZnO/CNTs) composites of large surface area and enhanced light assimilation range were produced for boosted hydrogen evolution from water. The photocatalysts were investigated for their morphological, structural, optical and photocatalytical properties. The photocatalytic activity of the composites was evaluated in pure water and in a mixture of water and methanol under simulated sunlight and visible light illumination. Under simulated sunlight irradiation, the maximum hydrogen generation rate of 925 μmolh^?1g^?1 from a combination of water and methanol was attained, which is almost 7 times higher than hydrogen generation rate achieved with pure ZnO. The VL-ZnO/CNTs photocatalyst resulted in hydrogen production rate of 267 μmolh^?1g^?1 from the water-methanol medium when exposed to visible light. This rate was about 3.5 folds lower than that achieved under simulated sunlight illumination. This improvement in hydrogen production rate is attributed to large surface area, high photo-response, better separation/transportation of the charge carriers and synergistic impact of V, La and CNTs in the designed photocatalyst.     

Ni3Mo3N coupled with nitrogen-rich carbon microspheres as an efficient hydrogen evolution reaction catalyst and electrochemical sensor for H2O2 detection

Hydrogen evolution reaction (HER) and electrochemical analysis are two important fields of electrochemical research at present. We found that both HER and some electrochemical analytical reactions relied on the concentration of hydrogen ions (H⁺) in solution, so we intended to develop an electrode material that is sensitive to H⁺ and can be used for both HER and some electrochemical analyses. In this work, we synthesized Ni₃Mo₃N coupled with nitrogen-rich carbon microspheres (Ni₃Mo₃N@NC MSs) as highly efficient electrode material for HER and detection of Hydrogen peroxide (H₂O₂), which plays an important role in physiological processes. Here the aniline was used as the nitrogen and carbon sources to synthesize Ni₃Mo₃N@NC. The Ni₃Mo₃N@NC MSs showed high performance for HER in 1 M KOH solution with a small overpotential of 51 mV at 10 mA cm^?2 and superior stability. For H₂O₂ detection, a detection limit of 1 μM (S/N = 3), sensitivity of 120.3 μA·mM^?1 cm^?2 and linear range of 5 μM–40 mM can be achieved, respectively. This work will open up a low-cost and easy avenue to synthesize transition metal nitrides coupled with N-doped carbon as bifunctional electrode material for HER and electrochemical detection.     

Rapid fabrication of Cu/Pd nano/micro-particles porous-structured catalyst using hydrogen bubbles dynamic template and their enhanced catalytic performance for formic acid electrooxidation

In this work, a self-supporting Pd–Cu bimetallic film with 3D porous structure was electrodeposited at the surface of glassy carbon electrode (GCE) using a facile double-template fabrication process, including hydrogen bubble templating method and galvanic replacement reaction, and its performance investigated as a catalyst for formic acid oxidation (FAO). The structure of the Cu/Pd porous film was characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The electrocatalytic activity of the as-prepared catalysts with high surface areas were evaluated in sulfuric acid solution containing 1 M formic acid using cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The Cu/Pd porous structure exhibited significantly high current densities of formic acid oxidation compared to the Cu/Pd particles film catalyst. The effects of galvanic replacement time and concentration of formic acid on the catalytic activity of as-prepared electrode for FAO were comparatively investigated.     

Integration of wind turbine with heliostat based CSP/CPVT system for hydrogen production and polygeneration: A thermodynamic comparison

In this study, two wind-solar-based polygeneration systems namely CES-1 and CES-2 are developed, modeled, and analyzed thermodynamically. CES-1 hybridizes a heliostat based CSP system with wind turbines while CES-2 integrates heliostat-based CPVT with wind turbines. This study aims to compare the production and thermodynamics performance of two heliostat based concentrated solar power technologies when hybridized with wind turbines. The systems have been modeled to produce, freshwater, hot water, electricity, hydrogen, and cooling with different cycles/subsystems. While the overall objective of the study is to model two polygeneration systems with improved energy and exergy performances, the performances of two solar technologies are compared. The wind turbine system integrated with the comprehensive energy systems will produce 1.14 MW of electricity and it has 72.2% energy and exergy efficiency. Also, based on the same solar energy input, the performance of the heliostat integrated CPVT system (CES-2) is found to be better than that of the CSP based system (CES-1). The polygeneration thermal and exergy efficiencies for the two systems respectively are 48.08% and 31.67% for CES-1; 59.7% and 43.91% for CES-2. Also, the electric power produced by CES-2 is 280 kW higher in comparison to CES-1.     

Pd electrodeposition on a novel substrate of reduced graphene oxide/ poly(melem-formaldehyde) nanocomposite as an active and stable catalyst for ethanol electrooxidation in alkaline media

Palladium nanoparticles (Pd NPs) were successfully electrodeposited on a reduced graphene oxide/poly(melem-formaldehyde) nanocomposite (rGO/PMF) NC as a catalyst for ethanol electrooxidation in alkaline media; melem was used as a nitrogen-rich source in the substrate structure for the first time. The specific surface area and average pore diameter of (rGO/PMF) NC were 481.61 m² gr^?1 and 10.23 nm, respectively. High nitrogen doping and structural defects improved the dispersion and anchoring of Pd NPs on (rGO/PMF) NC. The onset potential (E_onset) of Pd/(rGO/PMF) NC was shifted negatively to 110 mV, in comparison to Pd/rGO. Also, the current density and electrochemical active surface area (EASA) of Pd/(rGO/PMF) NC were enhanced to 44 mA cm^?2 and 67.58 m² gr^?1, respectively, as compared to Pd/rGO. Furthermore, the stability of Pd/(rGO/PMF)NC was indicated against ethanol oxidation intermediates during 7000 s. This work also produced a superior graphene-based material for direct ethanol fuel cell anode catalysts applications.