Alkaline Electrolysis Cell Research Articles

Cellular zirconia ceramics processed by direct emulsification

Highly porous zirconia ceramics for prospective use as separators in alkaline electrolysis cells have been processed by emulsification of paraffin in concentrated zirconia suspensions. Effects of processing parameters on porosity, cell size distribution, and pore interconnectivity are studied through Taguchi statistical design. The porosity of zirconia ceramics has shown a strong correlation with paraffin-to-suspension ratio employed in emulsification. High paraffin-to-suspension ratios combined with high gelatin content in the emulsion are beneficial for creating highly porous cellular materials with interconnected cell sizes. The attained microstructural features allow high percolation of ionic species in these highly porous ceramics after impregnation with aqueous electrolytes, facilitating charge transport within the liquid medium inside the ceramic bodies, as required for lower ohmic losses. This work provides guidelines for developing efficient ceramic separators for future use in alkaline electrolysis cells and other applications requiring thermally and chemically-stable ceramics with high and well-interconnected porosity.

Research on fuel cell energy storage control and power generation system

In order to realize the continuous stability of photovoltaic power generation system and the controllability of thermal energy storage, a photovoltaic fuel cell combined power generation system consisting of photovoltaic cell array, proton exchange membrane fuel cell, alkaline electrolysis cell and super capacitor is proposed. The system, at the same time, establishes the mathematical model of its various components and the system cost model, designs the thermal energy distribution of the thermal energy storage management coordination system, and uses the high efficiency battery to meet the load requirements of the power system. In addition, the paper uses simulation technology as a research method to build a simulation model of hybrid fuel cell thermal energy storage control and power generation system, and analyzes the system?s thermal energy supply and demand balance. The simulation results confirm that the photovoltaic fuel cell hybrid power generation system has high economic performance, can meet the user?s power and thermal energy requirements, and realizes the requirement of completely independent power supply.

Separators for alkaline water electrolysis prepared by plasma-initiated grafting of acrylic acid on microporous polypropylene membranes

Highly hydrophilic separators for alkaline water electrolysis were prepared by plasma-initiated grafting of acrylic acid on porous polypropylene (PP) membranes. The membranes were activated in a low-pressure radio-frequency discharge in oxygen and subsequently graft polymerization of acrylic acid was performed in aqueous solution. The membranes were characterized by gravimetric grafting degree (GD), SEM, FTIR, critical wetting surface tension (CWST) test, mechanical strength, and electrolytic conductivity. Moreover, the membranes were applied as separators in alkaline electrolysis cell, and content of hydrogen in the produced oxygen was measured to determine membrane permeability to hydrogen dissolved in the electrolyte. It was observed that increasing GD improves performance of membranes as separators in alkaline electrolysis, although the particular effects on the electrolytic conductivity and hydrogen permeability strongly depend on structure the of initial PP substrate. Ageing test conducted in 30 wt% KOH at 60 °C revealed that although considerable degrafting took place at beginning of the test, the remaining polyacrylic acid provided highly hydrophilic character to membrane for 7000 h of the test.

Tritium Extraction from Water

Tritiated wate`r production is ubiquitous in facilities that handle tritium gas. Sources range from decontamination efforts, to the deliberate conversion of elemental tritium to tritiated water in processes that strive to reduce emissions to the environment, to gaseous effluents to the environment. At low concentrations, ranging from a few μCi/L to mCi/L, high throughputs are required to process the high-volume, low-activity water. Combined electrolysis and catalytic exchange (CECE) shows promise by offering high throughput, reliability, economic viability, and facile coupling to isotopic separation systems if necessary. This paper will discuss the features of two production-scale CECE facilities: a 7 m3/h throughput system that uses an alkaline electrolysis cell and a 21 m3/h throughput system that uses a proton exchange membrane electrolysis cell. The former is in service and has been modified to improve reliability; the latter is in the initial stages of commissioning.

Feasible Capacity Ratio of H2 storage Using Electrolyzers and Batteries in Distributed Energy Systems Under Large-Scale Implementation of Solar Cells

Introduction The power grid controls their electric power supply by maintaining voltage, frequency, and transient stability, by predicting the electricity demand at any given time. However, recent large-scale implementation of photovoltaics (PV) makes it difficult to meet them because the gap between power supply and demand will be widening. The suppression of any power sources including solar power generation with sacrificing some electricity is sometimes adopted to avoid large-scale blackouts, and the situation is expected to be a common event at the 2030s. An effective solution to such situations is called as “leveling power”, which is the ability to maintain a balance between power supply and demand. Leveling power needs to be introduced not only into the centralized power grid but also into distributed energy systems. The major candidate of leveling power at distributed energy systems is electrochemical energy storage technology such as secondary batteries or hydrogen Power-to-Gas-to-Power (P2G2P). A smart energy system called Ene-swallow has been developed by our research group, and applied to Ookayama campus at the Tokyo Institute of Technology. This system manages 1400 kW-PV, 100 kW-FC, 70 kW gas engine and 100 kWh storage battery with a 10,000 kW-class electricity demand. Ene-Swallow also accumulates the power demand data in 1-sec intervals and PV power generation data in 1-min intervals. We previously carried out a techno-economic analysis of a hydrogen energy storage system to level the annual gap of power supply and demand [1]. Here we evaluated the potential of electrochemical energy storage as a leveling power with using the annual data from those data. Method We analyzed the current situation requirements for leveling power (analysis-1) and the applicability of a distributed energy storage system (analysis-2). For analysis-1, we analyzed 1-hour data of power generation and consumption published from power companies across Japan (Fig. 1a), and 1-min data of PV power generation (Fig. 1b) and 1-sec data of power demand (Fig. 1c) at Ookayama campus. For analysis-2, we set a tentative distributed grid with a 10,000 kW-class electricity demand, a given amount of primary power generation by PV and the power supply from the grid. In this work, we set no leveling power by the grid, which supplied constant power. Then, we determined the entire gap between power supply and demand during a single year based on the actual 1-minute data of PV power generation and power demand from April, 2017 to March, 2018. Then we estimated the required amount of energy storage, and thus determined the required number of P2G2P devices with alkaline electrolysis cell (AEC), solid oxide fuel cells (SOFC), H2 tanks and compressors, and lithium-ion batteries (LIB). In the system, the balance of power generation and consumption in a day is controlled as shown in Fig. 2. During the daytime, the surplus power from PV is leveled by an AEC. If AEC capacity is not sufficient, it is leveled by LIB. At night, the required power for demand is generated by an SOFC and/or an LIB. By optimizing the capacity of each component device in the distributed system, we evaluated the total system cost. We specified the expected technical parameters in the future (for the year 2030), such as unit price, efficiency and lifetime as shown in Table 1. Results From analysis-1, the 1-hour data showed that the supply fluctuation of PV power generation during the day strongly impacts the power grid when the energy mix ratio of PV to total annual demand reached about 10% when keeping nuclear power generation constant. The 1-minute data showed large fluctuations in PV generation within in a short time period (< 1 hr) during weather such as a cloudy day (Fig. 1b). Power fluctuations with different time scales have to be leveled by using electrochemical energy storage technologies. Analysis-2 showed that the total system cost could be reduced by using a combined system of P2G2P and LIB by utilizing their different characteristics. The combined system of P2G2P can reduce their total energy cost with dividing the role by power generation and the storage when the cost targets shown in Table 1 can be achieved. [Acknowledgements] A part of this study is supported by the New Energy and Industrial Technology Development Organization (NEDO) and MIRAI program of Japan Science and Technology Agency (JST). Reference [1] T.Okubo et al., 234th ECS Meeting AiMES 2018, (September 30-October 4, 2018) Figure 1

Enhanced Lifetime Cathode for Alkaline Electrolysis Using Standard Commercial Titanium Nitride Coatings

The use of hydrogen gas as a means of decoupling supply from demand is crucial for the transition to carbon-neutral energy sources and a greener, more distributed energy landscape. This work shows how simple commercially available titanium nitride coatings can be used to extend the lifetime of 316 grade stainless-steel electrodes for use as the cathode in an alkaline electrolysis cell. The material was subjected to accelerated ageing, with the specific aim of assessing the coating’s suitability for use with intermittent renewable energy sources. Over 2000 cycles lasting 5.5 days, an electrolytic cell featuring the coating outperformed a control cell by 250 mV, and a reduction of overpotential at the cathode of 400 mV was observed. This work also confirms that the coating is solely suitable for cathodic use and presents an analysis of the surface changes that occur if it is used anodically.

Feasible Energy System with Electrochemical Hydrogen Energy Storage for Leveling the Received Electricity at Large-Scale Solar Cell Installation

Introduction Recently, the large-scale installation of renewable energy is required to prevent global warming problem. Especially, the production cost of solar cell has drastically decreased recently. To install large-scale unstable power sources on renewable energy, the management of the gap between electricity demand and supply is a key issue. Thus, large-scale energy storage technologies have to progress to compensate the gap. As an energy storage, chemical energy of hydrogen is a promising candidate. Particularly in urban area, both “global hydrogen” and “local hydrogen” are required to supply sufficient energy to their huge energy demand. “Global hydrogen” is produced from low-cost primary energy globally and is transported for demand with a certain cost. “Local hydrogen” is produced by distributed energy system and is directly supplied without transportation. In the paper, we proposed a cost-competitive distributed energy system with the “local hydrogen” energy storage system. We analyzed the variation of total system cost by installing electrolysis cell (EC), fuel cell (FC) and secondary battery to compensate the gap due to electricity supply from large-scale solar cells (SC). We also proposed the appropriate SC arrangement for a middle size of distributed energy system. Method We evaluated the total system cost on the basis of real data from smart energy control system “Ene-Swallow”, developed by our research group, which manages the megawatt-scale distributed power sources in Tokyo Institute of Technology, Tokyo. The system has 1400 kW-SC, 100 kW-FC, 70 kW-gas engine and 100 kWh-lithium ion battery to manage the 10000 kW-scale electricity demand, which is suitable as a model for a middle-scale society with distributed power sources. The 650 kW-SC, which is almost half of total capacity of SC, is installed on the building (shown in Fig1) located in Tokyo. This building nearly achieves electricity self-sufficiency by the SC, 100 kW-FC and 70kW-gas engine. The building is covered with the “envelope of solar cells” (445 kW at the south wall, 40 kW at the west wall and 165 kW on the roof), where the maximum altitude in winter solstice is 31°. Global solar radiation in summer and winter are 15 MJ/m2 and 8 MJ/m2, respectively. Average temperature in summer and winter are 25°C and 5°C, respectively. In the location, the SCs on the building generates maximum electric power in winter because about 68% of SCs is installed at the south walls. The SC arrangement of the building has much smaller seasonal variation than typical arrangement on the roof to get better matching with the larger energy demands in winter. We constructed the energy system model to analyze the distributed energy system with electrochemical hydrogen energy storage and large-scale SC. In our model, the energy system with SC, alkaline EC, solid oxide FC, compressor, hydrogen tank and battery was assumed. Three hourly data from Apr/1/2016 to Mar/31/2017 were used (power generation from 750 kW-SC on the roofs, 650kW-SC on the building and electricity demand in the area). Based on these data, imaginary set of SC installation was assumed, where total amount of power generation from SC is equivalent to the electricity demand. Fig2 shows the energy flow in the model. In the daytime, the surplus electricity supplied from SC was assumed to be used for the production of hydrogen or battery charge. If the capacity of each device is not sufficient, the surplus electricity was assumed to be curtailed because it is hard to sell it in the future scenario with “large amount of solar energy”. In the night, the electricity to satisfy the demand was assumed to be generated by battery or FC. When the electricity supply is not enough, electricity was assumed to be purchased from an electrical grid. We carried out the energy balance simulation in the model by setting the capacities and technological parameters of devices. Finally, we analyzed the total system cost on the basis of the simulation. The analysis was carried out with the three cases of technology parameters of devices: (1) current (2015), (2) reduced SC price and (3) reduced all device prices (Table1). Result From the series of analysis, the total system cost can be reduced by installing the appropriate-scale hydrogen energy storage in the future. To achieve self-sufficiency ratio 100%, on the other hand, hydrogen tank cost drastically increased because its capacity got larger to absorb seasonal variation in power generation from SC. Controlling seasonal variation through SC arrangement can reduce the hydrogen tank cost. The cost-competitive system was proposed with the combination of hydrogen energy storage and SC arrangement. Figure 1

Oxygen Evolution Activity and Chemical Stability of Ni and Fe Based Perovskites in Alkaline Media

The electrochemical activity of LaNiO3, La0.97NiO3, LaNi0.6Fe0.4O3, La0.97Ni0.6Fe0.4O3 and La2Ni0.9Fe0.1O4, toward the oxygen evolution reaction (OER) was measured in 1M KOH at room temperature. All materials showed comparable OER activity with Tafel slopes in the range 56–98 mV/dec. The overvoltage at 10 mA·cm−2, measured on a well-defined geometric surface area, was in the range 0.38–0.45 V. The best performing materials among the ones investigated were LaNiO3 (multiphase) and La2Ni0.9Fe0.1O4. The chemical stability of the stoichiometric materials was also assessed in 31wt% and 45 wt% KOH respectively at 100°C and 220°C. All materials were partially decomposed after 1 week of exposure at 220°C. After 1 week of exposure at 100°C LaNiO3 had formed secondary phases whereas LaNi0.6Fe0.4O3 and La2Ni0.9Fe0.1O4 showed only traces of secondary phase. The main secondary phases were in all cases La(OH)3, NiO, Ni(OH)2 and Fe2O3. These observations indicate that the investigated oxygen electrode materials are not suitable for operation in alkaline electrolysis cells above 100°C.

Experimental and Numerical Study of the Effect of Gas-Shrouded Plasma Spraying on Cathode Coating of Alkaline Electrolysis Cells

The aim of this work is to improve the performance of electrodes prepared via atmospheric plasma spray by means of gas shrouding which is expected to apparently reduce the oxygen content of the plasma plume and subsequently improve the coating quality. Electrodes with dual-layer coating for alkaline water electrolysis were deposited on Ni-coated perforated substrates. Microstructure and morphology were studied by SEM. Element content was measured by EDS. Enthalpy probe was employed for measuring plasma temperature and velocity as well as the gas composition. For verifying and better understanding the shrouding effect numerical calculation was carried out according to the experimental settings. Electrochemical test was carried out to validate the shrouding effect. The results showed slight protecting effect of gas shrouding on plasma plume and the final coating. Over the dual-layer section, the measured oxygen fraction was 3.46 and 3.15% for the case without gas shrouding and with gas shrouding, respectively. With gas shrouding the coating exhibited similar element contents as the coating sprayed by VPS, while no obvious improvement was observed in the microstructure or the morphology. Evident electrochemical improvement was nevertheless achieved that with gas shrouding the electrode exhibited similar performance as that of the VPS-sprayed electrode.

Minimising the ohmic resistance of an alkaline electrolysis cell through effective cell design

The efficiency of an alkaline electrolysis cell depends strongly on its internal cell resistance, which becomes the dominant efficiency driver at high current densities. This paper uses Electrochemical Impedance Spectroscopy to decouple the ohmic resistance from the cell voltage, and, for the first time, quantify the reduction in cell resistance achieved by employing a zero gap cell configuration when compared to the conventional approach. A 30% reduction in ohmic resistance is demonstrated for the zero gap cell when compared to a more conventional design with a 2 mm electrode gap (in 1 M NaOH and at standard conditions). The effect on the ohmic resistance of operating parameters, including current density and temperature, is quantified; the zero gap cell outperforms the standard cell at all current densities, particularly above 500 mA·cm−2 Furthermore, the effect of electrode morphology on the ohmic resistance is investigated, showing that high surface area foam electrodes permit a lower ohmic resistance than coarser mesh electrodes. These results show that zero gap cell design will allow both low cost and highly efficient alkaline electrolysis, which will become a key technology for short term and inter-seasonal energy storage and accelerate the transition towards a decarbonised society.

Exergy Efficiency Analysis of a Power-to-Methane System Coupling Water Electrolysis and Sabatier Reaction

Power-to-methane (PtM) systems coupling solid oxide electrolysis cell (SOEC) and Sabatier reactors offers an efficient and promising pathway to integrate the renewable/nuclear power with the existing natural gas network. SOEC operates at a higher temperature and yet produce hydrogen or syngas with a controllable H2/CO ratio with higher efficiency compared to low temperature electrolyzers. Besides, with the coupling of the SOEC and the Sabatier reactor, methane can be synthesized in one reactor from renewable energy. In this study, we firstly compared the power-to-hydrogen processes using the alkaline electrolysis cell (AEC), the proton exchange membrane electrolysis cell (PEMEC) and the SOEC. A factor of 38% is used to convert electricity to primary energy for first law efficiency analysis. Exergy efficiency analysis is also carried out to distinguish the qualities of the heat, electricity and gaseous fuels. The results show the PtM system using SOEC is more efficient than those using the other electrolysis technologies due to lower overpotential and better heat coupling. Particularly, the intermediate temperate SOEC exhibits a better heat coupling with the Sabatier reactor rather than the high temperature SOEC to further improve the system efficiency. Figure 1

Exergy Efficiency Analysis of a Power-to-Methane System Coupling Water Electrolysis and Sabatier Reaction

The seasonal and intermittent features result in the renewable power curtailment. Seasonal power storage is required to utilize the curtailed renewable power. Power-to-methane (PtM) systems coupling solid oxide electrolysis cell (SOEC) and Sabatier reactors offers an efficient and promising pathway to integrate the renewable power with the existing natural gas network. SOEC operates at a higher temperature and yet produce hydrogen or syngas with a controllable H2/CO ratio with higher efficiency compared to low temperature electrolyzers. Besides, with the coupling of the SOEC and the Sabatier reactor, methane can be synthesized in one reactor from renewable energy. In this study, we firstly compared the power-to-hydrogen processes using the alkaline electrolysis cell (AEC), the proton exchange membrane electrolysis cell (PEMEC) and the SOEC. Exergy efficiency analysis is also carried out to distinguish the qualities of the heat, electricity and gaseous fuels. The results show the PtM system using SOEC is more efficient than those using the other electrolysis technologies at high current density due to lower polarization and better heat coupling. For SOEC, H2O/CO2 co-electrolysis coupling with methanation reactor exhibits a slightly lower exergy efficiency at low current density than H2O electrolysis coupling Sabatier reactor, but exceeds at high current density. At the H2O flow rate of 0.036 mol s-1 m-2 and H/C ratio of 5.5, a peak exergy efficiency of 75.66% is achieved at the current density of -5500 A m-2.

ChemInform Abstract: Zero Gap Alkaline Electrolysis Cell Design for Renewable Energy Storage as Hydrogen Gas

AbstractReview: 43 refs.

High Temperature and Pressure Alkaline Electrochemical Reactor for Conversion of Power to Chemicals

Moving away from fossil fuels requires harvesting more and more intermittent renewable energy resources and establishing a sustainable system for the production of chemicals. This brings forward the need for efficient large scale energy storage technologies 1-3 and technologies for the conversion of renewable electricity to chemicals. Electrochemical reactors can play a crucial role in this endeavor, since they can efficiently and reversibly transform electricity to high-value chemicals, and thus serve as energy storage and recovery devices for balancing the grid, while offering a means for the sustainable production of chemicals 4-6. A novel type of alkaline electrochemical cell that can operate at elevated temperature and pressure has been developed that relies on corrosion resistant high temperature diaphragms, based on mesoporous ceramic membranes where aqueous KOH is immobilized by capillary forces. Raising the operating temperature offers a means to boost performance, as both ionic transport and reaction kinetics are exponentially activated with temperature. Indeed, we have demonstrated alkaline electrolysis cells operating at 200-250 °C and 20-50 bar at very high efficiencies and power densities. This work will provide an overview of our efforts to develop components of such high temperature alkaline electrochemical reactors for different applications. Low-cost large-scale production methods have been successfully employed for the production of ceramic diaphragms and full cells. The influence of composition and microstructure on the long-term chemical stability and mechanical durability of the mesoporous ceramic membranes has been explored. Instrumentation for electrochemical testing at elevated pressures (up to 99 bar) and temperatures (up to 300 °C) with in-line chemical analysis has been established enabling experiments with gaseous or liquids reactants/products at cell sizes of up to 25 cm2. Efforts are currently directed towards the investigation of the intrinsic activity of mixed oxides for the oxygen evolution reaction at elevated temperatures and pressures, and of the intrinsic activity, selectivity and stability of supported metal catalysts towards the electrocatalytic conversion of biomass derivatives to high-value chemicals. Finally, the use of selected electrocatalysts for the production of high performance electrodes will be reported.

Nickel/Carbide Based Catalysts for Oxygen Evolution Reaction in Alkaline Solution

Hydrogen, produced by electrolysis, is one of the most promising means to store electricity coming from renewables and to address its intermittency. Due to the increase of global electricity share from renewable energy sources, large-scale storage systems are required. Alkaline electrolysis can be a suitable solution for the large-scale energy storage system. However, high overpotential and slow kinetics, particularly of the oxygen evolution reaction (OER), still limit the efficiency of the system. To enhance the efficiency of alkaline electrolysis cells, catalysts with high electrocatalytic activity for OER should be developed. Platinum-like behavior of tungsten carbide in surface catalysis was first discovered by Levy and Boudart in 1973[1]. In addition, tungsten carbide was reported to have a Pt-like electronic structure by Colton in 1975[2]. Since then, tungsten carbide has been studied widely and expected to replace noble metal catalysts which are used in many electrochemical reactions. In this study, we researched tungsten carbide as a support for nickel, and formation of bi-metallic surfaces for developing a high activity OER catalyst. WC was synthesized by two-steps. First, WC-Co was synthesized by heat treatment. Carbon nitride (g-C3N4) and tungsten chloride were used as a carbon and tungsten precursor. Cobalt precursor was also used to help carburization of tungsten. After synthesizing WC-Co, the acidic leaching process was followed by using sulfuric acid (H2SO4) to eliminate cobalt. Through additional mixing with 3d metal precursors and heat treatment, Ni/WC and NiFe/WC were synthesized. Furthermore, Ni/C was also prepared using same precursors as a counter group. Figure 1 shows the SEM images of the synthesized WC and Ni/WC. Cyclic voltammetry was performed to evaluate OER activity in 1 M KOH in potential range from 1 to 1.8 V. Figure 2 shows the OER catalytic activities of synthesized catalysts and Ir/C. Pure WC and Ni/C had 430 mV and 394 mV overpotential at 10 mA∙cm-2 respectively. In 3d Metal/WC cases, Ni/WC and NiFe/WC showed only 335 mV and 314 mV overpotential at 10 mA∙cm-2. Both catalysts had higher electrocatalytic activity for OER than Ir/C in alkaline media.

High Temperature Alkaline Electrolysis - Status and Potential

Alkaline electrolysis is a proven technology with several large scale facilities for hydrogen production realized and operated reliably for decades. Nevertheless, its broader deployment is hindered by the relatively high cost for hydrogen production. To overcome this obstacle, it is necessary to improve cell efficiency, increase the production rate, and decrease capital cost. Since conventional alkaline electrolysis technology has reached maturation, only small incremental improvements can be expected. To achieve a drastic step forward, we have developed a new generation of alkaline electrolysis cells that can operate at elevated temperature and pressure, producing pressurized hydrogen at high rate (m3 H2/hžm2 cell area) and high electrical efficiency. The concept relies on the development of corrosion resistant high temperature diaphragms, based on mesoporous ceramic membranes where aqueous KOH is immobilized by capillary forces, in combination with gas diffusion electrodes that overcome mass transport limitations at large production rates. Raising the operating temperature offers a means to drastically improve performance, as both ionic transport and reaction kinetics are exponentially activated with temperature. Indeed, we have demonstrated alkaline electrolysis cells operating at 200-250 °C and 20-50 bar at very high efficiencies and power densities. This enables high production rates near the thermoneutral voltage, thereby overcoming the need for cooling. This work will provide an overview of the exploratory technical studies undertaken so far. Two electrochemical test stations have been established to carry our experiments at elevated pressures (up to 99 bar) and temperatures (up to 300 °C). The conductivity of aqueous KOH was investigated at elevated temperatures to establish the optimum concentration at 200-250 °C. An optimum value of 0.84 S cm-1 was established at 200 °C for 45 wt% aqueous KOH immobilized in mesoporous SrTiO3. Gas diffusion electrodes were developed using metal foams loaded with different non-precious metal electrocatalysts in order to reduce the overpotentials for oxygen and hydrogen evolution. Small cells have been fabricated and operated at current densities of up to 1.75 A cm-2 and 3.75 A cm-2 at cell voltages of 1.5 V and 1.75 V at 200 °C at 20 bar, corresponding to electrical efficiencies of almost 99 % and 85 %, respectively. Long-term operation at 200 °C was successfully demonstrated for 400 h, suggesting relatively stable cell performance. Finally, low-cost production methods have been utilized for a first scale-up of the cell size from 1 cm2 to 25 cm2. Efforts are currently directed towards the investigation of the intrinsic activity of mixed oxides for the oxygen evolution reaction at elevated temperatures and pressures, and towards establishing the required infrastructure for testing of 25 cm2 cells.

Tungsten Carbide-Based Catalysts for Oxygen Evolution Reaction in Alkaline Media

Hydrogen produced by electrolysis is one of the promising means by which to store electricity coming from renewables and to address its intermittency. With the growing global electricity share from renewable energy sources, large-scale storage systems are required. Alkaline electrolysis can be a sustainable solution for the large-scale energy storage system. However, high overpotential and slow kinetics particularly of the oxygen evolution reaction (OER) still remains as a hurdle to limit efficiency of the system. To enhance efficiency of alkaline electrolysis cells, catalysts which have high electrocatalytic activity for OER should be developed. Platinum-like behavior of Tungsten carbide in surface catalysis was first reported by Levy and Boudart in 1973[1]. In addition, tungsten carbide was reported to have Pt-like electronic structure by Colton in 1975[2]. After that, tungsten carbide has been studied widely and expected to substitute noble metal catalysts which are used in many electrochemical reactions. Here, we studied tungsten carbide as a support for 3d-transition metals and make bi-metallic surfaces for developing a high activity OER catalyst. First, WC-Co was synthesized by heat treatment. Carbon nitride (g-C3N4) and tungsten chloride were used as a carbide precursor and cobalt acetate was also used for helping carbonization of tungsten. After heat treatment, acidic leaching process was followed to eliminate cobalt. Through additional mixing with Nickel precursor and heat treatment, Ni/WC was synthesized and to compare electrocatalytic activity Ni/C was also prepared. In addition, many different Ni/WC which have different Ni to WC ratios were synthesized and measured in electrochemical way. Finally, the optimal ratio was determined and it show better electrocatalytic activity than precious catalysts and any other non-noble catalysts. Cyclic voltammetry was measured to evaluate OER activity in 1 M KOH in potential range from 1 to 1.8 V. Figure 1 shows that pure WC and Ni/C have 394 mV and 413 mV overpotentials at 10 mA∙cm-2 respectively. In Metal/WC cases, Cobalt/WC shows only 417 mV. But Nickel/WC shows 340 mV overpotential at 10 mA∙cm-2 and higher electrocatalytic activity for OER than RuO2 in alkaline media. η @ 10 mA cm-2 (mV) Ni/C 394 WC 413 Co/WC 417 Ni/WC 340 RuO2 355 Table1. Activities for OER at 10 mA cm-2 References [1] R. B. Levy, M. Boudart, Science, New series, Vol. 181, No. 4099 (1973) 547-579 [2] Richard J. Colton, Jan-Tsyu j. Huang, J.Wayne Rabalais, Chemical Physics Letters, Vol. 34, No. 2 (1975) 337-339 Figure1. Cyclic voltammetry for the oxygen evolution reaction in 1 M KOH of Ni/C, WC, Co/WC, Ni/WC, RuO2 Figure 1

Electrochemical conversion of alcohols for hydrogen production: a short overview

In the emerging hydrogen economy, one of the major objectives is the production of electricity using fuel cells, particularly proton exchange membrane fuel cells (PEMFC). In this perspective, high purity hydrogen is needed. Hydrogen is currently mainly produced from fossil fuels (natural gas, oil, and coal) by energy‐consuming and environmentally unfriendly industrial processes that also involve complicated clean up steps for the removal of carbon monoxide and carbon dioxide. Water electrolysis (particularly the proton exchange membrane electrolysis technology, which allows higher efficiency than alkaline technology) appears to be a good candidate for the production of clean hydrogen. The use of renewable primary energy sources, such as wind, solar, tidal, etc., makes this technology greener. However, the low kinetics of water oxidation, which implies high cell voltage (i.e. high energy consumption) even when using noble metal‐based catalysts (Pt, Ru, Ir), makes this technology expensive. Biosourced alcohols can be interesting alternatives as hydrogen carriers in an electrolysis cell; their reversible oxidation potentials are much lower than that of water, ca 0.1 V versus SHE (standard hydrogen electrode) against 1.23 V versus SHE, so that the cell voltages for hydrogen production are lower (and so is the energy consumption). However, the low kinetics of alcohol oxidation in acidic media requires high Pt‐based catalyst loadings at the anode. Direct alcohol alkaline electrolysis cells can be operated with low Pt loading and even non‐noble metals. In the case of glycerol, generation of hydrogen at the cathode can be performed simultaneously with the formation of value‐added products at the anode for a more profit‐making process. WIREs Energy Environ 2016, 5:388–400. doi: 10.1002/wene.193This article is categorized under: Bioenergy &gt; Science and Materials Fuel Cells and Hydrogen &gt; Science and Materials Energy Efficiency &gt; Science and Materials

High Temperature Alkaline Electrolysis Cells with Metal Foam Based Gas Diffusion Electrodes

Alkaline electrolysis cells operating at 250°C and 40 bar are able to convert electrical energy into hydrogen at very high efficiencies and power densities. In the present work we demonstrate the application of a PTFE hydrophobic network and Ag nanowires as oxygen evolution electrocatalyst in the metal foam based gas diffusion electrodes. A novel cell production method, based on tape casting and hot pressing, was developed which allows to increase the cell size from lab scale (1 cm2) to areas of 25 cm2 or larger. The thickness of the electrolyte matrix could be adjusted to only 200 μm, achieving a serial resistance and total area specific resistance of only 60 mΩ cm2 and 150 mΩ cm2, respectively, at 200°C and 20 bar, yielding a record high current density of 3.75 A cm−2 at a cell voltage of 1.75 V. Encouraging long-term stability was obtained over 400 h of continuous electrolysis. This novel cell concept promises more than a 10-fold improvement in power density, compared to conventional alkaline electrolysis cells, and thereby equivalent reduction in stack size and cost.

Zero gap alkaline electrolysis cell design for renewable energy storage as hydrogen gas

Alkaline electrolysis using a zero gap configuration combines the efficiency of PEM with the cost efficiency of alkaline.