Water Electrolysis For Hydrogen Production Research Articles

Hydrogen bubble growth in alkaline water electrolysis: An immersed boundary simulation study

Enhancing the efficiency of industrial water electrolysis for hydrogen production is important for the energy transition. In electrolysis, hydrogen is produced at the cathode, which forms bubbles due to the diffusion of dissolved hydrogen in the surrounding supersaturated electrolyte. Hydrogen (and oxygen) bubbles play an important role in the achievable electrolysis efficiency. The growth of the bubbles is determined by diffusive and convective mass transfer. In turn, the presence and the growth of the hydrogen bubbles affect the electrolysis process at the cathode.In the present study, we simulate the growth of a single hydrogen bubble attached to a vertical cathode in a 30 wt% KOH solution in a cathodic compartment represented by a narrow channel. We solve the Navier–Stokes equations, mass transport equations and potential equation for a tertiary current distribution. A sharp interface immersed boundary method with an artificial compressibility method for the pressure is employed. To verify the numerical accuracy of the method, we performed a grid refinement study and checked the global momentum and hydrogen mass balances. We investigate the effects of flow rate and operation pressure upon bubble growth behaviour, species concentrations, potential and current density. We compare different cases in two ways: for the same time and for the same bubble radius. We observe that increasing the flow velocity leads to a small increase in efficiency. Increasing the operation pressure causes higher hydrogen density which slows down the bubble growth. For a given bubble radius, increasing the pressure leads to a small decrease in efficiency.

Anodized AlCoCrFeNi high-entropy alloy for alkaline water electrolysis with ultra-high performance

Alkaline water electrolysis (AWE) is a prospective method for producing green hydrogen to solve the energy crisis and reduce environmental pollution. However, the hydrogen production efficiency through this process is exceptionally low because the electrodes are expensive and inefficient. In this work, a kind of high-entropy alloy (HEA), bulk AlCoCrFeNi, is used as the efficient electrode for AWE. Results show that the HEA treated by 5-min fast anodization can achieve ultra-high catalytic activities for hydrogen and oxygen evolution reactions with low overpotentials of 880 and 845 mV to reach the current densities of −500 and 500 mA cm−2, respectively. For full water splitting, it only needs 3.00 V and exhibits excellent stability of more than 100 h at 500 mA cm−2. Our study demonstrates that the anodized AlCoCrFeNi HEA has promising applications as a highly efficient catalyst in industrial water electrolysis for hydrogen production, potentially addressing the energy crisis and environmental concerns.

Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni–Co Oxide Catalysts with Amorphous/Crystalline Surfaces

The development of high-performance oxygen evolution reaction (OER) catalysts based on earth-abundant transition metal oxides as alternatives to precious metal oxides is being pursued intensively for the large-scale application of alkaline water electrolysis for hydrogen production. Active OER electrocatalysts can be designed on the basis of fundamental insights into the catalytic phenomena occurring on surfaces. In particular, the temperature dependence of OER activity as a measure of reaction energies/barriers needs to be characterized by taking into account the operating temperature (60–80 °C) of a practical water electrolyzer. In this work, we synthesized Ni–Co oxide solid solution catalysts by the flame pyrolysis method, with particular emphasis on the temperature dependence of the OER catalysis, as a way to elucidate the catalytic reactions, from both experimental and theoretical perspectives. The as-prepared catalysts structured with conductive Ni–Co alloys were heat-treated at different temperatures in the presence of O2 to regulate the crystallinity of the oxide surfaces. The OER activity has been evaluated from 20 to 80 °C in 1 M KOH, and the OER kinetic current density was found to increase with increasing temperature for all catalysts obtained. Interestingly, the Ni–Co/oxide materials with amorphous or poorly crystalline oxide surfaces showed superior activity (3–8 times higher surface-specific activity at 1.55 V vs reversible hydrogen electrode (RHE)) than their crystalline counterparts at all temperatures. The OER activation energy also decreased with decrease of the crystalline oxide phases. It was demonstrated that the catalyst with amorphous Ni–Co oxide surfaces could be readily activated to form active oxyhydroxides under alkaline OER conditions. The amorphous or disordered structure of the surface oxide with low-coordinated sites is proposed to render the surface geometry energetically favorable for the rate-determining step O + OH → OOH, which accelerates the reaction kinetics and thus improves the OER activity, as explained by density functional theory calculations.

Efficient anodic biochar oxidation over three-dimensional self-support nickel-iron nanosheet on nickel foam in biochar-assisted water electrolysis for hydrogen production

Biochar-assisted water electrolysis (BAWE) facilitates the high-value utilization of biomass and energy-saving hydrogen production. However, the BAWE efficiency is hindered by slow kinetics of biochar oxidation reaction (BOR) at anode. Herein, to improve the overall efficiency of BAWE, three-dimensional porous nanosheets modified on nickel foam (Ni1Fe2-LDH@NF) was developed for BOR, and its mechanism was identified. Impressively, the BAWE system exhibited remarkable activity, including a low potential of 1.387 V vs. RHE for BOR over as-synthesized electrocatalyst at current density of 10 mA·cm−2, and excellent long-term stability over 20 h at a high current density of 200 mA·cm−2 and after 1000 CV cycles. The required electricity input was 3.29 kWh·Nm−3H2 at 10 mA·cm−2 for BAWE with Ni1Fe2-LDH@NF toward BOR. In addition, the reaction mechanism of BOR including biochar direct oxidation on the electrocatalysts surface and indirect oxidation in the electrolyte was deduced, according to the surface chemistry and composition changes of electrocatalysts and biochar, as well as the products. This work provides an effective strategy towards the enhancement of the BOR process by designing the binder-free electrocatalysts, and facilitates the development of BAWE for energy-efficient hydrogen production and biomass utilization.

Wet Gas Water Feed of Polymer Electrolyte Membrane Electrolyzer for Simultaneous Hydrogenation of Organic Chemical Hydride Energy Carrier and Water Decomposition

To utilize renewable electricity with fluctuation and localization, large-scale energy storage and transportation technologies using hydrogen energy carrier have been expected. In order to improve hydrogen energy carrier synthesis, we have studied one-step electrolysis for toluene electrohydrogenation and water decomposition using proton exchange membrane (PEM) electrolysis. This process has 1.09 V of theoretical decomposition voltage for simultaneous water electrolysis and toluene hydrogenation.As shown in Figure 1, anode reaction produces oxygen and proton, and proton transports cathode electrocatalyst layer through the PEM with water molecular. Water inhibits toluene transportation to reaction side and hydrogen evolution occurs as side reaction. We have reported electrolyzers that has cathode side of PEFC’s MEA like structure using PtRu/C and anode side of industrial electrolyzer like structure using mesh shape of DSE® electrode for oxygen evolution reaction, and sulfuric acid solution feeds as anolyte that is not only reactant but also for water management. Water back diffusion from cathode to anode enhances with sulfuric acid concentration. In addition, current efficiency with mesh type anode was higher than that with sintered fiber sheet type anode. The mesh shape of electrode makes current distribution that affects mass transfer pass distribution to improve current efficiency, although sheet type anode is lower overpotential because of large surface area [1 – 3]. As practical system, water transportation from anode to cathode should be supressed without sulfuric acid utilization, and electrochemical surface- area of anode should extend to reduce overpotential.In this study, we have investigated wet gas water feed for PEM electrolysis to reduce water transfer to cathode, because water transfer would control by relative humidity of wet gas that feed to anode for oxygen evolution reaction. Here, PEM water electrolysis type anode catalyst layer with ionomer was employed to reduce anode overpotential and to maintain ionic conduction in catalyst layer.Figure 1 shows the schematic drawing of toluene direct hydrogenation electrolyzers with water splitting. Figure 1 (a) is our conventional electrolyzer of H2SO4 solution feed, and Figure 1 (b) is wet air feed in this study. The anode side for wet air feed had polymer electrolyte fuel cell type serpentine gas flow channel. Anode catalyst layer was 1.0 mg cm-2 of IrOx (TKK) with Nafion ionomer. The porous transport layer was platinum plated sintered titanium sheet. PEM was Nafion 117 (Du Point), cathode catalyst layer was 0.5 mg cm-2 of PtRu/C with Nafion ionomer supported on a porous flow field of a carbon paper that was loaded 0.02 mg cm-2 platinum for chemical reaction of toluene and hydrogen.5 mL min-1 of toluene or 10% toluene – methylcyclohexane and 1.0 L min-1 of wet air fed to cathode and anode, respectively. Operation temperature was 80oC. After the 100 % RH feed electrolysis, there is no product except methylcyclohexane in the liquid phase and water transportation from anode to cathode reduced one twentieth from the conventional electrolyzer fed 1 M H2SO4 operation at 60oC. In this condition, IR free cell voltage of the wet gas fed electrolyzer was significantly smaller than that of the conventional one because of high surface area anode. Internal resistance of the wet gas feed determined by AC impedance method was about two times higher than that of the conventional, and current efficiency maintained in the low current density region. The internal resistance increased in the high current density region where the membrane and ionomer dry up with electro osmosis water. In this region, current efficiency also decreases.In summary, wet gas feed water electrolysis for electrohydrogenation of toluene using a PEM electrolyzer is an interesting technology that combines water electrolyzer with water purification system and manages water feed to reduce water transportation to cathode to maintain current efficiency of with accurate control of relative humidity and gas feed amount.AcknowledgementThis study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).References Nagasawa, K. Tanimoto, J. Koike, K. Ikegami, S. Mitsushima, J Power Sources, 439, 227070 (2019).Oi, K. Nagasawa, T. Takamura, Y. Misu, K. Matsuoka, S. Mitsushima, ECS Meeting s, MA2021-02, 1737 (2021).Mitsushima, Y. Sugita, J. Koike, Y. Kuroda, K. Matsuoka, Y. Sato, K. Nagasawa, ECS Meeting s, MA2020-02, 2494 (2020). Figure 1

Β-Feooh Nanorods As a Highly Active Self-Repairing Anode Catalyst for Alkaline Water Electrolysis Powered By Renewable Energy

The use of renewable energy as a primary energy source is urged because of the rapid progress of global warming. Because the renewable energy is unevenly distributed in terms of place and time, the production of hydrogen from renewable energy is crucial. Alkaline water electrolysis is a cost-effective technology for this purpose, though the degradation of electrodes under fluctuating power of renewable energy is recently regarded as a crucial problem. We have recently reported that a in-situ repair of anode catalyst (self-repairing catalyst), supplying fresh catalyst from electrolyte is quite useful to improve the lifetime under unsteady operation [1]. A hybrid cobalt hydroxide nanosheet (Co-ns) was used as the self-repairing catalyst, whereas its electrocatalytic activity is moderate. In this study, we demonstrate the use of β-FeOOH nanorods (β-FeOOH-nr) as a highly active and durable self-repairing catalyst. Because β-FeOOH-nr consists of iron as a metallic element, it is promising for its low cost and resource abundance. β-FeOOH-nr was synthesized by the coprecipitation of Fe3+ with tris(hydroxymethyl)aminomethane, followed by heating at 80 °C. The width and length of β-FeOOH-nr were 3–6 nm and 4–200 nm, respectively. The Fe K-edge XANES analysis showed that β-FeOOH-nr consists of Fe3+ species. Electrochemical tests were performed in a three-electrode PFA cell, using a nickel wire, a nickel coil, and a reversible hydrogen electrode, as working, counter, and reference electrodes, respectively. The β-FeOOH-nr was dispersed in 1 M KOH as an electrolyte. β-FeOOH-nr was first deposited on the nickel wire electrode by constant current electrolysis at 1 A·cm–2 for 240 min (30 min × 8 cycles). β-FeOOH-nr formed a thin layer of bundled nanorods and exhibited the oxygen evolution reaction (OER) overpotential of 320 mV at 100 mA cm–2, while previously reported Co-ns exhibited 342 mV. In addition, the activation of β-FeOOH-nr-coated electrode is almost finished at the first 30 min of the electrolysis, whereas Co-ns required 240 min for the activation. Because β-FeOOH-nr-coated electrode exhibited high OER activity with a small amount of β-FeOOH-nr deposited on the electrode, β-FeOOH-nr could activate electrode with shorted electrolysis time. The β-FeOOH-nr-coated electrode indicated the redox peak due to Ni2+/Ni3+ at 1.44 V vs. RHE which is at higher potential than that of a bare nickel electrode, implying that β-FeOOH-nr formed composite with active nickel species, such as Ni(OH)2 as highly active materials. The durability of the catalyst-coated electrode was examined in the presence of β-FeOOH-nr in the electrolyte by the newly reported shutdown-based accelerated durability test (SD-ADT) [2]. SD-ADT consists of multiple cycles of constant current electrolysis at 600 mA·cm–2 for 1 min and potential retainment at low potential of 0.5 V vs. RHE for 1 min. A bare nickel electrode is degraded only within 50 cycles by the SD-ADT (OER overpotential reached 640 mV at the 200th cycle), whereas β-FeOOH-nr-coated nickel electrode retained its low OER overpotential of 285 mV in at least 4000 cycles. Comparing with the SD-ADT in the absence of β-FeOOH-nr in the electrolyte, it was shown that β-FeOOH-nr was deposited during the SD-ADT to repair degraded electrode. In conclusion, β-FeOOH-nr was shown to be a useful anode catalyst for alkaline water electrolysis powered by fluctuating renewable energy. By dispersing β-FeOOH-nr in an electrolyte, the alkaline water electrolyzer can establish self-repairing system with very long lifetime under frequent potential change. The synchrotron radiation experiments were performed at the BL16B2 of SPring-8 with approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2021A5310). This work was supported by the JSPS KAKENHI (grant number 20H02821) from Ministry of Education, Culture, Sports, Science and Technology (MEXT) Japan. Part of this study uses outcomes of the development of fundamental technology for the advancement of water electrolysis hydrogen production in the advancement of hydrogen technologies and utilization projects (grant number JPNP14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO) in Japan.

Development and techno-economic evaluation of coal to ethylene glycol process and Allam power cycle and carbon capture and storage and integration process

Although coal is one of the primary energy sources in the world, the conversion and utilization process results in significant carbon emission and energy consumption. In addition to reducing reliance on oil, the coal to ethylene glycol process (CTEG) can encourage the diversification of energy use and continually meet market demand for ethylene glycol. It is strategically and practically significant in a broad sense. Reduced carbon emissions from CTEG processes are essential for the industry’s future growth in the context of global carbon neutrality. There were two innovative CTEG processes proposed: the novel coal poly-generation system for ethylene glycol process synthesis and electricity generation integrated with the Allam cycle (CTEG-AC) and the novel coal to ethylene glycol process integrated with the Allam cycle and water electrolysis for hydrogen production (CTEG-AEH). The simulation and modeling of the entire flowsheet were optimized together with the distribution ratio of the CO or syngas in these two processes. Then the techno-economic of the CTEG processes was compared with that of the traditional process. The results demonstrate that the total carbon dioxide emission of the CTEG processes was decreased by 84.81%, and the carbon efficiency of the CTEG-AC and CTEG-AEH processes was increased by 32.67% and 39.95%. Since the production cost and total capital investment of CTEG-AC decreased by 25.93% and 12.66% respectively, and the internal rate of return (IRR) increased by 4.47%, it had good economic benefits. The CTEG-AEH process, however, had the worst economic performance for its lowest income. Therefore, Allam cycle power generation technology with CO2 capture function can promote the low-carbon and economic development of the traditional CTEG process. It is necessary to effectively reduce the electricity consumption of the hydrogen production technology of water electrolysis, and then integrate it into the hydrogen shortage problem of the process.

Biochar sacrificial anode assisted water electrolysis for hydrogen production

Carbon-assisted water electrolysis uses carbon oxidation reaction replacing oxygen evolution reaction to decrease the anode potential and the energy consumption for water electrolysis hydrogen production. However, the mass transfer between carbon particle-electrolyte-anode limits its energy saving effect. Based on the principle of self-corrosion/oxidation of carbon-based electrode materials, the biochar sacrificial anode was proposed and investigated to solve the mass transfer issue in carbon slurry assisted water electrolysis for hydrogen production. Results showed that the activity and stability of sacrificial anode could be improved simultaneously in high concentration alkaline electrolyte using pinewood char as active substance, graphite as conductive agent and coal liquefying residue as binder. The biochar anode produced less oxygen than Pt anode, and the anode potential of biochar was 60–76% of that Pt anode. The application of biochar as sacrificial anode offers an industrial clean, scalable and sustainable idea to obtain green hydrogen.

Self-supporting copper electrode prepared by ultrasonic impact for hydrogen evolution reaction

Water electrolysis for hydrogen production requires highly active and inexpensive catalysts. Herein, we combine ultrasonic impact nanocrystallization (UIN) technology with nital etching method to rapidly prepare highly efficient self-supporting Cu electrode with abundant low-angle grain boundaries. When used as a catalyst for hydrogen evolution reaction (HER), the as-prepared electrode exhibits an overpotential of 353 mV at a current density of 10 mA cm−2, which is about 200 mV lower than that of the blank Cu plate. Moreover, the overpotential decreased to 246 mV after the stability test of 100 h, indicating a self-optimizing property. This work paves a new way for the preparation of self-supporting electrode with high performance.

Two-step coal-assisted water electrolysis for energy-saving hydrogen production at cell voltage of 1.2 V with current densities larger than 150 mA/cm2

The application of water electrolysis for hydrogen production is inhibited by high energy consumption, primarily due to the sluggish anodic oxygen evolution reaction (OER). Replacing OER with a thermodynamically favorable reaction is significant to decrease the energy consumption. Coal-assisted water electrolysis (CAWE), with a theoretical potential of only 0.21 V, received special attention. However, the conventional CAWE suffers from poor stability to maintain high current, the continuous collision of coal particles with electrodes and membranes also causes the abrasion of these components. Here, a two-step CAWE system with the electrolysis system (ES) and hydrothermal system (HS) was proposed. The homogeneous ES generates H2 assisted by the anodic Fe2+ oxidation (Fe2+→Fe3+), while the heterogeneous HS supplies Fe2+ via the reduction of Fe3+ by coal slurry (Fe3+→Fe2+). Results showed that key operating parameters significantly affected the Fe3+ reduction by coal in HS. Additionally, a homemade continuous proton exchange membrane electrolyzer was used to test the two-step CAWE concept. The current density can achieve 154 mA/cm2 and remain 136 mA/cm2 after 5 cycles, at a low cell voltage of 1.2 V, corresponding to a low power consumption of 2.87 kWh/Nm3(H2).

Enhanced oxygen evolution reaction kinetics through biochar-based nickel-iron phosphides nanocages in water electrolysis for hydrogen production

Highly-efficient and stable non-noble metal electrocatalysts for overcoming the sluggish kinetics of oxygen evolution reaction (OER) is urgent for water electrolysis. Biomass-derived biochar has been considered as promising carbon material because of its advantages such as low-cost, renewable, simple preparation, rich structure, and easy to obtain heteroatom by in-situ doping. Herein, Ni2P–Fe2P bimetallic phosphide spherical nanocages encapsulated in N/P-doped pine needles biochar is prepared via a simple two-step pyrolysis method. Benefiting from the maximum synergistic effects of bimetallic phosphide and biochar, high conductivity of biochar encapsulation, highly exposed active sites of Ni2P–Fe2P spherical nanocages, rapid mass transfer in porous channels with large specific surface area, and the promotion in adsorption of reaction intermediates by high-level heteroatom doping, the (Ni0.75Fe0.25)2P@NP/C demonstrates excellent OER activity with an overpotential of 250 mV and a Tafel slope of 48 mV/dec at 10 mA/cm2 in 1 M KOH. Also it exhibits a long-term durability in 10 h electrolysis and its activity even improves during the electrocatalytic process. The present work provides a favorable strategy for the inexpensive synthesis of biochar-based transition metal electrocatalysts toward OER, and improves the water electrolysis for hydrogen production.

(Invited) Leak Current Analysis of Stop Operation and Its Modeling for the Development of Bipolar Alkaline Water Electrolyzer Electrodes

Introduction Water electrolysis is expected a key device to introduce large-scale renewable electricity under management of power grid and electrification of non-electric sector. While alkaline water electrolysis (AWE) systems are well-developed large system, degradation under fluctuated operation with start and stop operation is significant issue to combine photovoltaic and/or wind turbine generation is significant issue. In this study, we have been investigated reverse current, which is leak current through manifold of bipolar alkaline water electrolyzers, and electrode potential behavior of stop operation, and proposed accelerated durability test (ADT) protocol for start and stop operation. Experimental and modeling Figure 1 shows configuration of 4-cells bipolar alkaline water electrolyzer that was consisted with end plates of EP(-) and EP(+), bipolar plates of BP1 to BP3, anodes, separators, and cathodes with principle of reverse current. The end and bipolar plates were made of nickel. Anodes and cathodes were commercially available oxygen and hydrogen electrocatalyst coated nickel mesh electrodes (De Nora Permelec Ltd) with 27.8 cm2 of projected area. Zirfon Perl UTP500 (Agfa) was used for separators. Manifolds were made of Teflon tubes and 15 mL/min of 7 M (= mol/dm3) was circulated for each anolyte and catholyte chambers during measurements. An anode and a cathode set on a bipolar plate. During operation anodes and cathodes are oxidized and reduces, respectively. After stop, the anode and the cathode on a bipolar plate connects both electronically and ionically, so oxidized anode and reduced cathode surface discharges to same potential. In this study, we measured electrode potential and reverse current after 1 h water electrolysis of 80oC at 0.6 A/cm2. The reverse current was measured ionic current through communicating tube with D. C. clamp meter (KEW2510, Kyoritsu).Reverse current behavior was analyzed with COMSOL Multiphysics version 5.5 based 2-dimensional model of stack and height direction using experimentally anode and cathode potentials as functions of discharge for anode and cathodes. Results and discussion Figure 2 shows cell performances in the stacks and a picture of the lab-scale zero-gap configuration electrolyzer. All cells in a stack showed almost the same performance. The cell voltage was 2 V at 400 mA/cm2 at 30oC and was 1.8 V at 500 mA/cm2 at 80oC. Therefore, we think all cells and parts work well.Figure 3 shows reverse currents and electrode potentials as a function of time after 1 h electrolysis under 600 mA/cm2 at 30 or 80 oC. Here, the dashed lines in Fig. 3-a) were simulated value and were almost same after 20 s. The measured reverse current increased around 20 s. At this moment, outlet manifolds filled with electrolyte to increase ionic conduction among the chambers, which was not considered in the simulation. After degassed of manifolds, the reverse current decreased with time with the largest reverse current for the BP2. The reverse current at 80oC was significantly larger than that at 30oC. This difference could be explained the dependence of ionic resistance of manifold on temperature. At same moment, anode and cathode potentials on the end plates were almost constant. The anode cathode potentials on the bipolar plates decreased and increased with time, respectively. Both anode and cathode showed significantly potential change region. The final potentials of all electrodes were around 0.9 V vs. RHE. The potential change regions of the electrodes on the BP2 were earlier than others. Here, the anode and cathode potentials as functions of discharge were almost same for the electrode on all bipolar plates. Therefore, the average discharge functions for anode and cathode were treated as characteristics of electrodes of this study. Using this function, reverse current as a function of time could be expressed accurately using the developed model. From this model, reverse current, and electrode potentials as a function of time would be expected with discharge function of each electrode and ionic resistance of manifold.Figure 4 shows that a start & stop operation simulated ADT protocol based on bipolar electrolyzer measurements. We propose the combination of constant current electrolysis, potential sweep, and chronoamperometry as the inset of illustration in Fig. 4, because constant current measurement is easier to get reproductivity in high current that need accurate iR correction for constant potential measurement and current control measurement never simulate stop operation. Acknowledgements This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Sulfur-doped NiCo carbonate hydroxide with surface sulfate groups for highly enhanced electro-oxidation of urea

NiCo-based hydroxides are promising catalysts for urea oxidation reaction. To further enhance their catalytic performance, the combined effect of nonmetal heteroatom doping and surface functional groups on their catalytic behaviors deserves to be evaluated. Herein, as a proof of concept, both the sulfur-doped NiCo(OH)2CO3 with surface sulfate groups (SS-NiCo) and the surface-sulfated NiCo(OH)2CO3 (S-NiCo) are synthesized by hydrothermal method. The effect of sulfur doping and surface sulfate treatment on the morphology, crystal structure, electronic structure and electrochemical properties is comprehensively studied. It is found that both the incorporation of sulfur into the crystal structure and the introduction of surface sulfate groups can tune the electronic structure and thus promotes the intrinsic activity of the NiCo(OH)2CO3. Additionally, the surface sulfate groups can effectively reduce the series resistance and thus enhance the charge transfer/reaction kinetics. The optimized SS-NiCo catalyst delivers a current density of 100 mA cm−2 at 1.34 V vs RHE, which is much smaller than those of the S-NiCo (1.38 V) and the pristine NiCo(OH)2CO3 (1.43 V). In addition, the SS-NiCo catalyst shows good performance in the urea-assisted water electrolysis for hydrogen production.

Transient behaviors and mathematical model of proton exchange membrane electrolyzer

The transient characteristics of proton exchange membrane water electrolysis for hydrogen production are crucial for the study of the load control and durability of the electrolyzer under the fluctuating conditions of renewable energy sources. In this study, a dynamic model of the electrolyzer is established based on various equivalence theories used to describe the transient characteristics of the electrolyzer during operation. Differential-equation-based transient models of the RC (resistance and capacitance) equivalent circuit and the equivalent controlled current source, their advantages and disadvantages, and their typical transient response spectra are presented. Among these, the graphical method based on the polarization curve is recommended because it has the advantages of intuitive and simple expression and can help researchers precisely and efficiently predict the response form and time of current or voltage using various control methods. The transient characteristics of the shutdown process reflect electrochemical processes similar to those of fuel cells in the electrolyzer during the OCV (open circuit voltage) period. The performance of the transient process is related to the structure of the electrolyzer and the operating conditions of the measurement. Low-voltage sustenance with manual intervention following shutdown may have a positive effect on the durability of the electrolyzer.

Polymeric membrane materials for green hydrogen production by water electrolysis: Progress and suggestions for future development

<p indent="0mm">Green hydrogen has gained much interest due to its low cost, sustainability, and environmental friendliness, especially when combined with water electrolysis technology powered by renewable energy resources. It has been recognized as one of the perfect solutions to achieve the goal of near-zero carbon emissions. According to the type of materials used to separate the anode and cathode and the ionic species it conduct, the electrolyzers can be divided into several categories, i.e., alkaline water electrolyzer (AWE) that involve the use of liquid electrolyte, proton exchange membrane water electrolyzer (PEMWE), solid oxide electrolyzer (SOE), and anion exchange membrane water electrolyzer (AEMWE). As the key component in different water electrolysis technologies, polymeric membrane materials, including proton exchange membrane (PEM), anion exchange membrane (AEM), and ion-solvating membranes (ISM), are of great importance, which serve as the ionic conductor and gas separator. Thus, the efficiency and durability of water electrolyzers are mainly determined by the properties of membranes, such as ionic conductivity, chemical stability, and mechanical properties. However, these unfavorable performance parameters of membranes still limited the worldwide commercialization of water electrolysis for the production of green hydrogen. In a typical AWE, a porous diaphragm made of asbestos or composite ceramic (or asbestos)/polymer materials (Zirfon, a state-of-the-art diaphragm) is used to separate the gas product and transport hydroxide ions. Although the mature AWE technology shows higher durability, low capital cost, and high compatibility with non-noble metal catalysts, they operate at low current densities lying between <sc>0.3−0.4 A cm⁻²,</sc> owning to the high ionic resistance and high gas permeation of the non-ionic separator membranes. The replacement of porous diaphragm with ionic polymeric membranes, such as PEM, AEM, and ISM based on polybenzimidazoles have attracted increasing attention in water electrolysers, due to their effectiveness of ion transport and gas tightness of the dense membrane. The acidic PEM allow the operation of water splitting with higher efficiency and current densities <sc>(500−2000 A cm⁻²).</sc> However, large-scale implementation of PEMWE technology is limited by the expensive PEM and precious platinum group metal (PGM) catalysts. When working under basic environment, the AWE using solid AEM and ISM combines the merits of traditional AWE and PEMWE, i.e., an alkaline working environment allows for the use of PGM-free catalysis and the solid hydroxide ion conducting membrane reduce the ionic resistance of the cells. Thus, the design of AEM and ISM materials plays a crucial role in the overall performance and durability of electrolytic cells. Currently, compared with PEMWE, the AEMs and ISMs with sufficient conductivity and satisfactory stability are still highly needed, due to the well-recognized vulnerable functional cations and polymer backbones in hot and alkali aqueous solutions. Thus, numerous chemical designs on AEMs are carried out. In this review, we summarized the research progress of polymeric membranes in water electrolysis for hydrogen production. We first compared the properties of membranes and electrolyzer device performance using different types of membranes, and analyzed the relationship between polymer structure and device performance; then, after analyzing the development and the technical advantages and disadvantages of PEM, AEM, and ISMs, the technical limitations and future developing trends of these technical routes were discussed. Finally, we also give a brief prospect on how to guide and encourage the future development of various technical pathways through the policy guidance, so as to realize the large-scale market penetration of water electrolysis technology for green hydrogen production.

NiFe nanosheets as urea oxidation reaction electrocatalysts for urea removal and energy-saving hydrogen production

The preparation of high-performance electrocatalysts is a breakthrough to solve the increasingly prominent problems of environmental degradation and energy depletion. Urea oxidation reaction (UOR) plays a vital role in treating urea-rich wastewater and assisting hydrogen production with low energy consumption. To alleviate the sluggish intrinsic reaction kinetic barrier of six-electron transfer involved in UOR, we develop a NiFe ultra-thin two-dimensional nanosheet array supported on nickel foam as UOR electrocatalyst by one-step hydrothermal method. Benefiting from the in-situ synthesis strategy, abundant mesoporous structure, and the electronic structure change of Ni after the introduction of Fe, NiFe nanosheets (NiFe NSs) exhibit remarkable UOR catalytic activity and excellent long-term stability. Moreover, we assemble a two-electrode electrolytic cell with NiFe NSs/NF as the anode. The results show that the cell voltage of urea assisted water electrolysis for hydrogen production decreased by 15.2% rather than the regular water splitting, as well as that the urea concentration in electrolyte is degraded 55.6% after electrolysis for 36 h at 1.70 V. This work indicates a feasibility verification for the electrocatalytic removal of urea in wastewater treatment, and an efficient and energy-saving method for urea-assisted electrolytic hydrogen production based on NiFe nanosheets.

Kinetics and oxidation pathways of Fe3+-catalyzed carbon-assisted water electrolysis for hydrogen production

Carbon-assisted water electrolysis can significantly reduce the electricity consumption of electrolytic hydrogen production, but its slow kinetics limit its further development. In-depth investigation of the oxidation pathways and control steps of coal particles during electrolysis can help to improve the reaction rate in a more targeted manner. In this study, the electrochemical activities of several different ranks of coal, activated carbon, and graphite are compared, and the electrooxidation process is disentangled to investigate the kinetic characteristics of the oxidation of solution catalysts, the reaction of coal with solution catalysts and the electrooxidation of coal. Structural characterization is used to investigate the key factors affecting the electrochemical activity. The results show that coal particles mainly undergo indirect oxidation during electrolysis, and direct oxidation only accounts for a small fraction of oxidation; the oxidation of the solution catalyst on the electrode surface is reversible, and the controlling step in the whole process is the redox reaction between the solution catalyst and coal particles. A variety of oxygen-containing functional groups are generated on the surface of coal particles after electrolysis, among which the C-O group plays a more critical role in the oxidation activity.

Optimal scheduling strategy of electricity‐heat‐hydrogen integrated energy system under different operating modes

With the increasing penetration level of renewable energy in the integrated energy system (IES), water electrolysis for hydrogen production (WEHP) technology has become an effective solution to increase the capacity of renewable energy utilization. Therefore, this paper proposes to take WEHP and hydrogen fuel cell (HFC) as flexible resources to participate in the optimal scheduling of IES under grid-connected/off-grid operation mode. Firstly, focusing on the production, storage and utilization of hydrogen energy, a unified operation model of WEHP module is built by analyzing the differences of the three WEHP technologies. And then, “co-generation” model of HFC, the residual capacity and transportation cost model of hydrogen storage device (HSD) are built. Second, by analyzing the uncertainty of light intensity and wind speed, a prediction error correction method is proposed to improve the prediction data accuracy of renewable energy power generation. Third, taking the lowest daily operation cost as the objective function, the optimal scheduling model of electricity-heat-hydrogen integrated energy system under grid-connected/off-grid operation mode is constructed. On this basis, the operation scheduling model of electricity-heat-hydrogen integrated energy system is transformed into a mixed integer linear model by piecewise linearization method, and the model is solved by CPLEX solver. Finally, an example is given to verify the rationality of the proposed scheduling model in the grid-connected/off-grid operation mode. On one hand, reasonable optimal scheduling of multiple WEHP combination is helpful to reduce the daily operation cost of IES. On the other hand, by correcting the prediction data deviation of renewable energy power generation, the equipment output of electricity-heat-hydrogen integrated energy system can be more reasonable, which is helpful to reduce the daily operation cost and improve the operation reliability. The effects of sensitive factors such as the penetration level of renewable energy, the relative fluctuation of electricity price and hydrogen price on the operation cost of optimal scheduling scheme are further analyzed, which provides a theoretical reference for the optimal scheduling of IES.

Hydrogen production from offshore wind power in South China

Wind power hydrogen production is the direct conversion of electricity generated by wind power into hydrogen through water electrolysis hydrogen production equipment, which produces hydrogen for convenient long-term storage through water electrolysis. With the development of offshore wind power from offshore projects, construction costs continue to rise. Turning power transmission into hydrogen transmission will help reduce the cost of offshore wind power construction. This paper analyses the methods of producing hydrogen from offshore wind power, including alkaline water electrolysis, proton exchange membrane electrolysis of water, and solid oxide electrolysis of water. In addition, this paper outlines economic and cost analyses of hydrogen production from offshore wind power. In the future, with the development and advancement of water electrolysis hydrogen production technology, hydrogen production from offshore wind power could be more economical and practical.

A Low-Cost Metal-Free Graphite Felt Electrode for Coal-Assisted Water Electrolysis for Hydrogen Production

Cheap, active and stable electrodes are vital for coal-assisted water electrolysis for hydrogen production (CAWE). Conventional CAWE uses relatively costly metal-based anodes such as Pt, SnO2/Ti, and IrO2-RuO2/Ti. Previous work confirms that metal-free carbon anodes, however, demonstrate excellent performance in biomass-assisted water electrolysis. Inspired by this, this work examines the feasibility and effectiveness of low-cost graphite felt (GF) anodes in CAWE. The results show that GF is a promising candidate for CAWE. Compared to Pt, SnO2/Ti, Pt/Ti, IrO2-RuO2/Ti, and IrO2-Ta2O5/Ti, GF has higher reactivity for the CAWE. The current density is higher than 5 mA cm−2 when the cell voltage is 1 V for coal electrolysis at Pt∥GF. When the current density is 1 mA cm−2, 5 mA cm−2, 10 mA cm−2, and 50 mA cm−2, the cell voltage of water electrolysis at Pt∥IrO2-RuO2/Ti is 1.84 times, 1.64 times, 1.50 times and 1.13 times that of coal electrolysis at Pt∥GF, respectively. Compared with precious metal-based electrodes, GF electrodes used for CAWE can greatly reduce the cost. Therefore, this study provides important guidance for the industrial development of CAWE.