Hydrogen Gas Generation Research Articles

Synthesis of Copper Nanoparticles Supported over Graphene-like Material Composite as a Catalyst for Hydrogen Evolution

The need for an alternative energy source that is both clean and abundant has led to research into a hydrogen economy. Hydrogen gas can be produced slowly via the hydrolysis of sodium borohydride (NaBH4). A catalyst can be used to speed up the rate at which hydrogen is produced, however many catalysts involve relatively expensive materials like precious metals. This study explores a novel copper nanoparticle supported on a graphene-like material composite as a catalyst for the hydrolysis of NaBH4. The material was characterized via powdered X-ray diffraction (P-XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and Energy Dispersive spectroscopy (EDS). The P-XRD confirmed the crystallinity structures of graphene-like material (GLM) and copper nanoparticles supported over graphene-like material (CuGLM). The P-XRD spectra indicated the (110), (111), and (200) lattice planes of copper nanoparticles. In FTIR analysis, the shifted and sharpening functional group peaks were observed when copper nanoparticles were supported by the GLM template. The TEM result indicated that the copper nanoparticle had a size of approximately 10 nm. The catalyst (CuGLM) was tested under different doses of NaBH4, solution pH, and reaction temperatures. Temperature data were used to determine the activation energy of the reaction to be 46.8 kJ mol−1, which is competitive when compared to similar catalysts. The catalyzed reaction generated the highest volume of hydrogen at pH 8 (51 mL), 303 K (32 mL), and 1225 μmol of NaBH4 (37 mL). The catalyst was found to be able to be used multiple times in succession without any significant loss in hydrogen generated. This catalyst is an exciting option for the sustainable generation of hydrogen gas as a fuel source.

Exploration of the dual fuel combustion mode on a direct injection diesel engine powered with hydrogen as gaseous fuel in port injection and diesel-diethyl ether blend as liquid fuel

The present study explores the possibilities of the use of diesel-diethyl ether (DDEE) blends as pilot fuel, and hydrogen (H2) as inducted gaseous fuel in a diesel engine operated on dual fuel mode (DFM). DEE was added to diesel in ratios of 5–25% in increasing steps of 5%, to prepare the DDEE5, DDEE10, DDEE15, DDEE20, and DDEE25 blends that were used as pilot fuel. In this current study, for hydrogen gas generation, a hydrogen production kit was fabricated which was powered by solar energy. The hydrogen gas was produced from the electrolysis of water-KOH solution. During the experiment, hydrogen was inducted through the engine intake port employing an electronic gas injector. The quantity of hydrogen injection was set constant of 0.2 lpm for all the test cases. DDEE-hydrogen (DDEE+H2) blends accomplished overall good results compared to diesel. DDEE20+H2 furnished optimal results compared to diesel and other DDEE+H2 blends. Peak cylinder pressure for DDEE20+H2 was 66.91 bar at 5.2oCA aTDC, and the maximum HRR was 32.75 J/deg.CA. Compared to diesel, the BTE of engine for DDEE20+H2 was augmented by about 0.6% and the BSFC was diminished by about 3.7%, at maximum load conditions. A decline in CO and HC emissions of 29.6%, and 35% were observed for DDEE20+H2 at maximum load condition, but the NO and CO2 emanation was observed to be higher by around 29.4%, and 17.4% in comparison to diesel respectively.

Lessons learned from in situ corrosion experiments in the HADES URL

Abstract A wide range of metals have been studied as a candidate container material to be considered in the geological disposal concept of high-level radioactive waste and spent fuel in Belgium. More than 40 years ago, SCK CEN started studies on the corrosion of these metals. The HADES underground research laboratory (URL) played an important role in the corrosion research as it enabled in situ corrosion experiments to be carried out that simulate realistic disposal conditions as closely as possible. These experiments consisted of placing metallic coupons on a steel support tube, heated from the inside, that was installed in Boom Clay, thereby exposing the coupons to various conditions representative of the disposal concept that was considered at that time. Test durations lasted from 6 months to approximately 7.5 years. This paper summarizes the results from the various corrosion studies and discusses their implications in the choice of disposal concept. One of the main outcomes of these experiments was a change of rationale regarding the choice of the container material from carbon steel (corrosion-allowance) to stainless steel (corrosion-resistant). The main arguments for this change were the need to avoid severe pitting corrosion during the aerobic period and to minimize the generation of hydrogen gas during the subsequent anaerobic period.

Synthesis of NiMoO4/NiMo@NiS Nanorods for Efficient Hydrogen Evolution Reactions in Electrocatalysts.

As traditional energy structures transition to new sources, hydrogen is receiving significant research attention owing to its potential as a clean energy source. The most significant problem with electrochemical hydrogen evolution is the need for highly efficient catalysts to drive the overpotential required to generate hydrogen gas by electrolyzing water. Experiments have shown that the addition of appropriate materials can reduce the energy required for hydrogen production by electrolysis of water and enable it to play a greater catalytic role in these evolution reactions. Therefore, more complex material compositions are required to obtain these high-performance materials. This study investigates the preparation of hydrogen production catalysts for cathodes. First, rod-like NiMoO4/NiMo is grown on NF (Nickel Foam) using a hydrothermal method. This is used as a core framework, and it provides a higher specific surface area and electron transfer channels. Next, spherical NiS is generated on the NF/NiMo4/NiMo, thus ultimately achieving efficient electrochemical hydrogen evolution. The NF/NiMo4/NiMo@NiS material exhibits a remarkably low overpotential of only 36 mV for the hydrogen evolution reaction (HER) at a current density of 10 mA·cm-2 in a potassium hydroxide solution, indicating its potential use in energy-related applications for HER processes.

Experimental Investigation and Modelling by Machine Learning Techniques for Hydrogen Generation by Reacting Aluminium with Aqueous NaOH Solution

Hydrogen gas is projected as the future fuel for energy generation due to high energy density, and almost zero COx and NOx emissions during combustion. Production of H2 gas by the chemical reaction of aluminium and aqueous NaOH solution appears to be a simple and cost effective technique. Accurate forecasting of the reaction kinetics based on multi-variable interactions is necessary for large scale in-situ production and control of hydrogen gas. In the present study, the kinetics of the reaction between Al and aq. NaOH to produce H2 at different temperatures and concentrations of NaOH is investigated. Data obtained from these investigations are used to predict the reaction rate and correlate the simulated and experimental results using Machine Learning Techniques, viz, Artificial Neural Network (ANN) and Multiple Linear Regression (MLR). The simulation model obtained by the MLR technique is found to be less accurate in terms coefficient of correlation than the ANN model while comparing with the experimental results. The coefficient of correlations (Rcc) and average absolute relative error % are found to be 0.998 and 1.377% respectively during simulation by ANN. During the ANN simulation, 97.8 % of data points lie within a 95 % level of confidence indicating very good simulation capability. The results of the investigation reveal the application of Machine learning technique for the accurate prediction of hydrogen gas generation by a chemical reaction.

The anoxic corrosion of mild steel in a cementitious repository environment

AbstractThe long‐term disposal of low‐ and intermediate‐level radioactive waste is anticipated to involve the encapsulation of the material within a cementitious matrix before placement in a deep geological repository. After sealing, the waste repository will become anoxic and the corrosion of emplaced metals will result in the production of hydrogen gas. Knowledge of the rate at which this hydrogen is generated is valuable in that it permits the assessment of pressure build‐up within the repository. The corrosion behavior of mild steel has been monitored through the generation of hydrogen gas, under simulated repository conditions that mimic various stages of cement evolution. It was found that, when cement is used to encapsulate steel, the passage of several years is required for the steel and cement to reach a steady hydrogen production rate. Steel that is directly immersed in simulated cement pore water requires only months to stabilize. All measured steel uniform corrosion rates were significantly below 1 nm year−1 at 50°C, regardless of the test environment, after more than 4 years of exposure.

3D nanostructured nickel film supported to a conducting polymer as an electrocatalyst with exceptional properties for hydrogen evolution reaction

A two-layer system was applied to a nickel substrate for use as the electrocatalyst of the hydrogen evolution reaction (HER) in a phosphate buffer solution. It was comprised of a three-dimensional (3D) porous underlayer of nickel nanoparticles with a size of less than 35 nm, followed by an electrodeposited top layer of poly (aniline-co-pyrrole). The underlayer and top coating were both synthesized by applying a constant potential to a three-electrode system. The catalyst characterization was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectrometry. The electrocatalytic activity of the fabricated electrodes was measured by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry. The electrode exhibited an overpotential of 520 mV at a current density of 10 mA cm−2, comparable to 530 mV of platinum. Furthermore, the Tafel slope of the electrode was 90 mV dec−1, almost equal to that of platinum. This exceptional performance was explained by the synergistic interaction between 3D-Ni and poly (aniline-co-pyrrole) layers. Such a synergism was demonstrated by the fact that the resulting electrode lacked substantial catalytic activity when each of these two layers was deposited on the substrate alone. The Nyquist diagrams revealed that the 3D-Ni film resulted in minimal charge transfer resistance, allowing fast kinetics of HER. The coupling of this property with the ability of the polymer to adsorb H+ ions led to the high electrocatalytic activity of the proposed electrode. This electrode performed better than platinum, which was a promising result. This indicated that a lower voltage input was required to generate hydrogen gas using the prepared electrode.

Efficient Self-Powered Overall Water Splitting by Ni4 Mo/MoO2 Heterogeneous Nanorods Trifunctional Electrocatalysts.

The exploration of cost-effective multifunctional electrodes with high activity toward energy storage and conversion systems, such as self-powered alkaline water electrolysis, is very meaningful, although studies remain quite limited. Herein, a heterogeneous nickel-molybdenum (NiMo)-based electrode is fabricated for the first time as a trifunctional electrode for asymmetric supercapacitor (ASC), hydrogen evolution reaction, and oxygen evolution reaction. The trifunctional electrode consists of Ni4 Mo and MoO2 (denoted Ni4 Mo/MoO2 ) with hierarchical nanorod heterostructure and abundant heterogeneous nanointerfaces creating sufficient active sites and efficient charge transfer for achieving high performance self-power electrochemical devices. The ASC consists of the as-prepared Ni4 Mo/MoO2 positive electrode, showing a broad potential window of 1.6V, and a maximum energy density of 115.6Whkg-1 , while the alkaline overall water splitting (OWS) assembled using the as-prepared Ni4 Mo/MoO2 as bifunctional catalysts only requires a low cell voltage of 1.48V to achieve a current density of 10mAcm-2 in aqueous alkaline electrolyte. Finally, by integrating the Ni4 Mo/MoO2 -based ASC and OWS devices, an aqueous self-powered OWS is assembled, which self-power the OWS to generate hydrogen gas and oxygen gas, verifying great potential of the as-prepared Ni4 Mo/MoO2 for sustainable and renewable energy storage and conversion system.

Monolithic Nickel Catalyst Featured with High-Density Crystalline Steps for Stable Hydrogen Evolution at Large Current Density.

Producing hydrogen via electrochemical water splitting with minimum environmental harm can help resolve the energy crisis in a sustainable way. Here, this work fabricates the pure nickel nanopyramid arrays (NNAs) with dense high-index crystalline steps as the cata electrode via a screw dislocation-dominated growth kinetic for long-term durable and large current density hydrogen evolution reaction. Such a monolithic NNAs electrode offers an ultralow overpotential of 469mV at a current density of 5000mA cm-2 in 1.0m KOH electrolyte and shows a high stability up to 7000 h at a current density of 1000mA cm-2 , which outperforms the reported catas and even the commercial platinum cata for long-term services under high current densities. Its unique structure can substantially stabilize the high-density surface crystalline steps on the catalytic electrode, which significantly elevates the catalytic activity and durability of nickel in an alkaline medium. In a typical commercial hydrogen gas generator, the total energy conversion rate of NNAs reaches 84.5% of that of a commercial Pt/Ti cata during a 60-day test of hydrogen production. This work approach can provide insights into the development of industry-compatible long-term durable, and high-performance non-noble metal catas for various applications.

Proton nuclear magnetic resonance (1H NMR) of flammable organic chemicals in radioactive high-level supernatant waste at the Savannah River Site (SRS).

The Savannah River Site stores approximately 36 million gallons of radioactive and hazardous waste that contains approximately 245 million curies. The waste is sent through various chemical processes to reduce its volume and to separate various components. The facility plans to replace formic acid (a chemical used to reduce soluble mercury) with glycolic acid. Recycle solution with glycolate may flow back to the tank farm, where the glycolate can generate hydrogen gas by thermal and radiolytic mechanisms. The current analytical method for detecting glycolate (ion chromatography) in supernatant requires a large dilution to reduce interference from the nitrate anions. Hydrogen nuclear magnetic resonance is an analytical method that requires less sample dilution. It takes advantage of the CH2 group in glycolate. Liquid samples were spiked with four different levels of glycolate to build a calibration line, as it is recommended in the standard addition method. The detection and quantitation limits determined were 1 and 5ppm, respectively, for 32 scans, which is well below the process limit of 10ppm. In one test, 800 scans of a supernatant spiked with 1ppm glycolate resulted in a -CH2 peak with a signal-to-noise ratio of 36.

Surface plasmon assisted photocatalytic hydrogen generation with Ag decorated g-C3N4 coupled SnO2 nanophotocatalyst under visible-light driven photocatalysis

Photocatalytic hydrogen evolution from water is a feasible technique to solve energy crises and reduce dependance on carbon fuels. As for this, silver nanoparticles were grown on the surface of SnO2 coupled g-C3N4 nanocomposite for the generation of hydrogen gas from water under visible light photocatalysis. The prepared samples were properly characterized to investigate their light absorption characteristics followed by charge generation and separation for water splitting. The optimized nanocomposite produced 270 μmol h−1 g−1 hydrogen which was much superior to pure g-C3N4 and SnO2. These upgraded photocatalytic activities were attached to the extended visible-light absorption due to the presence of Ag nanoparticles characterized by surface plasmon resonance (SPR) and suitable conduction bands position of g-C3N4 and SnO2 for the separation of excited charges. The photoluminescence study, amount of produced hydroxyl free radicals and electrochemical investigation confirmed the long-rooted charge separation capability of the nanocomposites. We believe that this work will have more positive impacts on the synthesis of low cost SPR assisted photocatalysts for energy production and environmental purification.

A novel device to generate green electric energy by water splitting at room temperature: Enhancing the efficacy by tuning nickel oxide thru lithium substitution

The present work reports a novel device that generates energy simply by water splitting and requires no other external energy source. Generating green energy by hydroelectric cell (HEC) from water splitting is an emerging concept in the field of energy harvesting. Efficient non-photocatalytic splitting of water molecules at room temperature produces green electricity even without sunlight. The synthesized pure and lithium (Li) substituted nickel oxide (NiO) is an oxygen deficient mesoporous material and is reported for the first time for this application. Using an electrolytic chain reaction, the reported material dissociates water into H3O+ and OH- ions, generating a potential across electrodes. The tuned ratio of 80% nickel and 20% lithium (Li20Ni80O) based HEC produced 135 mA at 1.06 volts using a pellet radius of 1.75 cm. This provides a significant peak power (Pout) of 143 mW. The material is characterized using X-ray spectroscopy and Electron Paramagnetic Resonance spectroscopy for oxygen vacancies. Photoluminescence (PL) confirms the defect states formed by Ni2+ interstitials. Mesoporosity and surface areas are observed by Brunauer Emmett Teller (BET). The ionic diffusion due to splitting of H3O+ and OH- ions is observed with Nyquist curves. Nickel oxide is a cost-effective and ecologically sustainable solution for green energy generation. The energy generated per square meter by this method is comparable to solar cell energy with the added advantage of generating energy in the dark as well. Since, byproduct of this process is the generation of hydrogen gas, this material can also be used for hydrogen production. This technology may lead to an alternative route in the power sector.

Hydrogen generation by soluble CO2 reaction with zero-valent iron or scrap iron and the role of weak acids for controlling FeCO3 formation

This study points out a new perspective on CO2 sequestration and H2 gas generation in a system of either zero-valent iron (Fe0) or scrap iron along with NaHCO3 and citric acid. Under a high bicarbonate environment, micro-size Fe0 (5–40 g/L) is oxidized at mild anaerobic conditions, generating hydrogen gas with a production rate in the range of 0.09–0.55 g(H2)/kg(Fe0)·h. At the same conditions without bicarbonate, the generation of H2 was negligible. At the end of the reaction, the pH was alkaline so it can be used to absorb CO2. Carbonate ions create a passivation layer on the Fe0 surface, called siderite (FeCO3), that entrapped Fe0 and hindered H2 production. By comparing citric, oxalic, and ascorbic acids for their ability to remove the siderite layer, citric acid was found to be the most effective. In a system of scrap iron-NaHCO3/citric acid, for seven consecutive cycles, it was found that by replacing the media solution with a new media after the end of each cycle and flushing with CO2 in the beginning of each cycle resulted in higher than 85 vol% H2 after one day of exposure and higher than 94 vol% H2 at the end of each cycle.

Modular Access to Quaternary α-Hydroxyl Acetates by Catalytic Cross-Coupling of Alcohols

Quaternary α-hydroxyl acids and their derivatives have attracted considerable attention because of their unique and broad functionalities. Herein, we successfully established a selective and modular protocol to access quaternary α-hydroxyl acetates via dehydrogenative cross-coupling of 1,2-diols and primary alcohols by using tris-N-heterocyclic carbene iridium (tris-NHC-Ir, 0.05 mol %) complexes as catalysts and Ba(OH)2 as the base, along with the generation of byproducts water and hydrogen gas. A plausible mechanism involving dehydrogenation of alcohols, aldol-condensation, and 1,2-alkyl rearrangement reactions was proposed, in which 1,2-alkyl rearrangement was responsible for the construction of the quaternary carbon center.

Evolving a New Electron Transfer Pathway for Nitrogen Fixation Uncovers an Electron Bifurcating-Like Enzyme Involved in Anaerobic Aromatic Compound Degradation.

Nitrogenase is the key enzyme involved in nitrogen fixation and uses low potential electrons delivered by ferredoxin (Fd) or flavodoxin (Fld) to reduce dinitrogen gas (N2) to produce ammonia, generating hydrogen gas (H2) as an obligate product of this activity. Although the phototrophic alphaproteobacterium Rhodopseudomonas palustris encodes multiple proteins that can reduce Fd, the FixABCX complex is the only one shown to support nitrogen fixation, and R. palustris Fix- mutants grow poorly under nitrogen-fixing conditions. To investigate how native electron transfer chains (ETCs) can be redirected toward nitrogen fixation, we leveraged the strong selective pressure of nitrogen limitation to isolate a suppressor of an R. palustris ΔfixC strain that grows under nitrogen-fixing conditions. We found two mutations were required to restore growth under nitrogen-fixing conditions in the absence of functional FixABCX. One mutation was in the gene encoding the primary Fd involved in nitrogen fixation, fer1, and the other mutation was in aadN, which encodes a homolog of NAD+-dependent Fd:NADPH oxidoreductase (Nfn). We present evidence that AadN plays a role in electron transfer to benzoyl coenzyme A reductase, the key enzyme involved in anaerobic aromatic compound degradation. Our data support a model where the ETC for anaerobic aromatic compound degradation was repurposed to support nitrogen fixation in the ΔfixC suppressor strain. IMPORTANCE There is increasing evidence that protein electron carriers like Fd evolved to form specific partnerships with select electron donors and acceptors to keep native electron transfer pathways insulated from one another. This makes it challenging to integrate a Fd-dependent pathway such as biological nitrogen fixation into non-nitrogen-fixing organisms and provide the high-energy reducing power needed to fix nitrogen. Here, we show that amino acid substitutions in an electron donor for anaerobic aromatic compound degradation and an Fd involved in nitrogen fixation enabled electron transfer to nitrogenase. This study provides a model system to understand electron transfer chain specificity and how new electron transfer pathways can be evolved for biotechnologically valuable pathways like nitrogen fixation.

Experimental investigation of simultaneous hydrogen production and desalination via electrodialysis process

The primary purpose of the electrodialysis (ED) process is to desalinate saline water; besides this, hydrogen, a valuable energy carrier gas, is generated at the cathode side of the ED cell in this study. However, hydrogen gas reacts with oxygen gas and reforms water due to the internal recirculation of the electrolyte solution from the anode to the cathode compartment. This study investigates the potential of hydrogen gas generation in an ED system that desalinates sodium sulfate (Na2SO4) solution. The maximum conductivity removal ratio is 98.1% when ion-exchange resins are placed into the diluate compartment at pH 8, and the ED system's hydrogen production rate is 76.8 mg H2/h·kg Na2SO4. The maximum hydrogen production rate is achieved as 118.8 mg H2/h·kg Na2SO4 solution under 14.06 mA/cm2 current density. The maximum energy and exergy efficiencies are calculated as 25.29% and 28.78%, respectively. The results indicate that the conventional ED process makes hydrogen production possible while desalinating saline water.

Chemical looping gasification of biomass char for hydrogen-rich syngas production via Mn-doped Fe2O3 oxygen carrier

Because of its low cost, an iron-based oxygen carrier is a promising candidate for hydrogen-rich syngas production from the chemical looping gasification of biomass. However, it needs modification from a reactivity point of view. In this study effect of Mn doping on Fe2O3 has been investigated for hydrogen-rich syngas production from biomass char at different temperatures (700–900 °C) and steam flow rates (60–100 μL/min). Several techniques (XRD, XPS, BET, and TPR-H2) have been utilized to characterize fresh and spent oxygen carriers. The result demonstrated Mn-doing boosted the redox activity and the amount of oxygen vacancies, which increased hydrogen gas generation. Hydrogen production displayed different behavior across temperatures due to detecting Fe2O3 and MnFeO3 phases for spent oxygen carriers. For the Fe2O3 oxygen carrier hydrogen gas yield is 1.67 Nm3/kg which is due to reduction of Fe2O3 phase to Fe3O4. However, the MnFe2O4 spinel phase detected in the spent MnFeO3 oxygen carrier is a reason for improving hydrogen gas yield to 1.84 Nm3/kg. Change reaction temperature from 900 °C to 850 °C reduced hydrogen gas yield from 1.84 Nm3/kg to 1.83 Nm3/kg for with MnFeO3 oxygen carrier. Regarding different steam flows, the proper flow rates that can maintain the formed phases and obtained best hydrogen gas yield are 80 and 90 μL/min, respectively. Meanwhile, the best hydrogen gas yield (2.21Nm3/kg) are obtained with MnFeO3 oxygen carrier at optimum conditions (850 °C and 90 μL/min).

Two-Dimensional Benzobisthiazole-Vinylene-Linked Covalent Organic Frameworks Outperform One-Dimensional Counterparts in Photocatalysis

Vinylene/olefin-linked two-dimensional covalent organic frameworks (v-2D-COFs), featured with vinylene-linked in-plane conjugations, high chemical stabilities, and designable chemical structures, are promising for optoelectronic/photocatalytic applications. Developing v-2D-COFs with superior π-conjugation and optoelectronic properties is meaningful but remains challenging. In this work, we present the crystalline benzobisthiazole-bridged unsubstituted v-2D-COF (v-2D-COF-NS1 and v-2D-COF-NS2) synthesized via a benzothiazole-mediated aldol-type polycondensation. Interestingly, the resultant v-2D-COF exhibits a high chemical stability under both strong acidic (12 M HCl) and basic conditions (saturated KOH) due to the robust vinylene-linked skeletons. Moreover, the electron-deficient thiazole units and 2D π-conjugations endow v-2D-COFs (i.e., v-2D-COF-NS1) a narrow band gap of ∼1.85 eV with a conduction band of −3.65 eV vs vacuum, which are desirable for photocatalytic hydrogen evolution. As such, the v-2D-COF-NS1-based photoelectrode gives a photocurrent up to ∼47 μA cm–2 at 0.3 V vs reversible hydrogen electrode (RHE), which is much higher than the value of the corresponding linear polymer (LP-NS1) and outstanding among the reported COF photoelectrodes. Under a continuous visible light irradiation, v-2D-COF-NS1 generates hydrogen gas with an excellent rate of ∼4.4 mmol h–1 g–1 over 12 h. This work demonstrates the synthesis of unsubstituted v-2D-COFs that intrinsically contain benzobisthiazole-based building blocks and shows great potential in photocatalytic reactions.

Towards the quantification of the chemical mechanism of light-driven water splitting on GaN photoelectrodes.

We present results from a study addressing the unbiased water-splitting process and its side reactions on GaN-based photoelectrodes decorated with NiOx, FeOx, and CoOx nanoparticles. Observations involving physicochemical analyses of liquid and vapour phases after the experiments were performed in 1 M NaOH under ambient conditions. A water-splitting process with GaN-based photoelectrodes results in the generation of hydrogen gas and hydrogen peroxide. Quantification of the water-splitting chemical mechanism gave numerical values indicating an increase in the device performance and restriction of the GaN electrocorrosion with surface modifications of GaN structures. The hydrogen generation efficiencies are ηH2(bare GaN) = 1.23%, ηH2(NiOx/GaN) = 4.31%, ηH2(FeOx/GaN) = 2.69%, and ηH2(CoOx/GaN) = 2.31%. The photoelectrode etching reaction moieties Qetch/Q are 11.5%. 0.21%, 0.26% and 0.20% for bare GaN, NiOx/GaN, FeOx/GaN, and CoOx/GaN, respectively.

Fatigue free relaxor ferroelectric and electrocatalytic hydrogen evolution of yttrium substituted BaBi2Nb2O9 layered structured nanoceramics for energy storage application

Lead-free bismuth layered structured ferroelectric ceramics are highly important in superior energy storage applications. The slim hysteresis curve with high energy storage density and efficiency is expected for wide application. In this regard, the suitable electrocatalyst for the generation of hydrogen gas through water-splitting show high importance as an alternative energy source. The current article aims to investigate the above goals by incorporating 5% yttrium at the place of bismuth for BaBi 2 Nb 2 O 9 relaxor ferroelectrics. The solid-state synthesized method successfully prepared the single-phase material and is confirmed through spectroscopic and morphological analysis. The dielectric characteristics follow diffused phase transition with broad temperature dependence that indicated the space charge polarization in the material owing to the presence of Y 3+ at different domains. The higher degree of diffuseness and low dielectric loss implies the significant role of charge carriers during frequency and temperature variation in the dielectric study. Impedance spectroscopy analysis indicates the non-Debye type relaxation and NTCR behavior of the material that is correlated to the multiple relaxation processes. The slim P-E hysteresis curve and fatigue-free properties of the materials up to 10 6 cycles reflect its usefulness in the potential device as NVRAM applications. The materials are also used for hydrogen evolution reaction (HER) under an electrochemical condition. A lower overpotential value of 180 mV is obtained at 10 mA cm −2 current density. The lower Tafel slope and charge transfer resistance value support its superior HER activity. The above results demonstrated the potential application of the studied material (BaBi 1 · 9 Y 0 · 1 Nb 2 O 9 ) in the energy storage application and as an electrocatalyst for alternative energy source.