Hydrogen production by a low-cost electrolyzer developed through the combination of alkaline water electrolysis and solar energy use

Electrolysis is a relatively simple process for obtaining hydrogen and can be combined with use of renewable energy sources, such as solar photovoltaic energy, for clean, sustainable gas production. This study designed a cylindrical electrolytic cell made of acrylic and 304 stainless steel electrodes to produce hydrogen. The electrolyte used was sodium hydroxide (NaOH 2–5 mol L^?1), and the direct current voltages applied were 2.0, 2.7, and 3.4 V. The maximum hydrogen production was achieved with 5.0 mol L^?1 NaOH and 3.4 V electric voltage. The system was connected to a photovoltaic panel of 20 W and exposed to solar radiation from 10 a.m. to 2 p.m. Approximately 2 L of hydrogen was produced within a period, and an average irradiance of 800.0 W m^?2 ± 60 W m^?2 was achieved. The system was stable throughout the tests.     

Benefits of external heat sources for high temperature electrolyser systems

High Temperature ELectrolysers (HTEL) operate around 1073 K with steam at 1073 K. Water is previously heated up in the Balance of Plant by the hot outlet gases and optionally by electrical heaters. If liquid water is fed to the system, vaporisation needs are covered by electrical heating, which leads to a low system efficiency of 89% vs. HHV. Using steam instead of liquid water would suppress vaporisation needs, thus increase the efficiency. This work aims to analyse the potential benefits of a steam supply. Calculation is performed without considering the energy required to preheat water. Results show that feeding the system with low-temperature steam instead of liquid water enables a system efficiency jump of 18%. Further increasing the steam temperature to 933 K negligibly impacts the system efficiency and is therefore unnecessary. It is concluded that a low-temperature steam source is sufficient to increase significantly the HTEL system efficiency.     

Direct coupling of an electrolyser to a solar PV system for generating hydrogen

Hydrogen as an energy currency, carrier and storage medium may be a key component of the solution to problems of global warming, poor air quality and dwindling reserves of liquid hydrocarbon fuels. Hydrogen is a flexible storage medium and can be generated by the electrolysis of water. It is particularly advantageous if an electrolyser may be simply and efficiently coupled to a source of renewable electrical energy. This paper examines direct coupling of a polymer electrolyte membrane (PEM) electrolyser to a matched solar photovoltaic (PV) source for hydrogen generation and storage. Such direct coupling with minimum interfacing electronics would lead to substantial cost reduction and thereby enhance the economic viability of solar-hydrogen systems. The electrolyser is designed for fail-safe operation with multiple levels of safety and operational redundancy. A control system in the electrolyser unit provides for disconnection when required and for auto-start in the morning and auto shut-down at night, simultaneously addressing the goals of minimum energy loss and maximum safety. The PV system is a 2.4 kW array (20.4 m² total area) comprising 30, 12 V, 80 W, Solarex polycrystalline modules in a series–parallel configuration. The integrated system has been operated for approximately 60 days over a 4-month period from September 2007 to January 2008 with many periods of unattended operation for multiple days, experiencing weather ranging from hot and sunny (above 40 °C) to cool and cloudy. The principle and practicality of direct coupling of a suitably matched PV array and PEM electrolyser have been successfully demonstrated. Details of electrolyser operation coupled to a PV array along with modelling work to match current–voltage characteristics of the electrolyser and PV system are described.     

Performance of a high temperature polymer electrolyte membrane water electrolyser

A high temperature polymer electrolyte membrane water electrolyser (PEMWE) was investigated at temperatures between 80 and 130 °C and pressures between 0.5 and 4 bar. Nanometer size Ru_0.7Ir_0.3O₂ and Pt/C were employed as anode and cathode catalysts respectively. The catalyst coated on membrane (CCM) method was used to fabricate the membrane electrode assemblies. The membrane, oxygen evolution catalysts and MEAs were characterized with SEM, XRD and TEM. The influence of high temperature and pressure was investigated using in situ electrochemical measurements. Increasing temperature and pressure produced higher current densities for oxygen evolution, and smaller terminal voltages. The high temperature PEMWE achieved a voltage of 1.51 V at a current density of 1 A cm⁻², at 130 °C and 4 bar pressure.     

Experimental investigation of a solar tower based photocatalytic hydrogen production system

In this paper, production of hydrogen from concentrated solar radiation is examined by a laboratory scale solar tower system that is capable of handling continuous flow photocatalysis. The system is built and studied under a solar simulator with an aiming area of 20 × 20 cm². The fraction of solar spectrum useful for water splitting depends on the energy band gap of the selected photocatalyst. Two types of nano-particulate photocatalysts are used in this work: ZnS (3.6 eV) and CdS (2.4 eV). The effect of light concentration on photocatalysis performance is studied using Alfa Aesar 99.99% pure grade, 325 mesh ZnS nano-particles. An improved quantum efficiency of 73% is obtained as compared to 45% with the same sample under non-concentrated light in a previous study. Only 1.1% of the energy of the solar radiation spectrum can be used by ZnS catalyst. A mixture of CdS and ZnS nano-particulate photocatalysts (both Alfa Aesar 99.99% pure grade, 325 mesh) is used to conduct a parametric study for a wider spectrum capture corresponding to 18% of the incident energy. Hydrogen production increases from 0.1 mmol/h to 0.21 mmol/h when the operating conditions are varied from 25 °C and 101 kPa to 40 °C and 21 kPa absolute pressures. Furthermore, the implementation of a continuous flow process results in an improvement in the energy efficiency by a factor of 5.5 over the batch process.     

Theoretical model and experimental analysis of a high pressure PEM water electrolyser for hydrogen production

This work aims at analysing the performances of a prototype of a high pressure Polymer Electrolyte Membrane water electrolyser.     

Performance assessment of a solar hydrogen and electricity production plant using high temperature PEM electrolyzer and energy storage

This paper investigates the performance of a high temperature Polymer Electrolyte Membrane (PEM) electrolyzer integrated with concentrating solar power (CSP) plant and thermal energy storage (TES) to produce hydrogen and electricity, concurrently. A finite-time-thermodynamic analysis is conducted to evaluate the performance of a PEM system integrated with a Rankine cycle based on the concept of exergy. The effects of solar intensity, electrolyzer current density and working temperature on the performance of the overall system are identified. A TES subsystem is utilized to facilitate continuous generation of hydrogen and electricity. The hydrogen and electricity generation efficiency and the exergy efficiency of the integrated system are 20.1% and 41.25%, respectively. When TES system supplies the required energy, the overall energy and exergy efficiencies decrease to 23.1% and 45%, respectively. The integration of PEM electrolyzer enhances the exergy efficiency of the Rankine cycle, considerably. However, it causes almost 5% exergy destruction in the integrated system due to conversion of electrical energy to hydrogen energy. Also, it is concluded that increase of working pressure and membrane thickness leads to higher cell voltage and lower electrolyzer efficiency. The results indicate that the integrated system is a promising technology to enhance the performance of concentrating solar power plants.     

Life cycle assessment of high temperature electrolysis for hydrogen production via nuclear energy

A life cycle assessment (LCA) of one proposed method of hydrogen production—the high temperature electrolysis of water vapor—is presented in this paper. High temperature electrolysis offers an advantage of higher energy efficiency over the conventional low-temperature alkaline electrolysis due to reduced cell potential and consequent electrical energy requirements. The primary energy source for the electrolysis will be advanced nuclear reactors operating at temperatures corresponding to those required for the high temperature electrolysis. The LCA examines the environmental impact of the combined advanced nuclear-high temperature electrolysis plant, focusing upon quantifying the emissions of carbon dioxide, sulfur dioxide, and nitrogen oxides per kilogram of hydrogen produced. The results are presented in terms of the global warming potential (GWP) and the acidification potential (AP) of the system. The GWP for the system is 2000 g carbon dioxide equivalent and the AP, 0.15 g equivalents of hydrogen ion equivalent per kilogram of hydrogen produced. The GWP and AP of this process are one-sixth and one-third, respectively, of those for the hydrogen production by steam reforming of natural gas, and are comparable to producing hydrogen from wind- or hydro-electricity powered conventional electrolysis.     

Development and operation of alternative oxygen electrode materials for hydrogen production by high temperature steam electrolysis

High temperature steam electrolysis (HTSE) is one of the most promising ways for hydrogen mass production. To make this technology suitable from an economical point of view, each component of the system has to be optimized, from the balance of plant to the single solid oxide electrolysis cell. At this level, the optimization of the oxygen electrode is of particular interest since it contributes to a large extent to the cell polarization resistance. The present paper is focused on alternative oxygen electrode materials with improved performances compared to the usual ones mainly based on perovskite structure. Two nickelates, with compositions La₂NiO_4+δ and Nd₂NiO_4+δ are investigated and evaluated in HTSE operation at the button cell level. The performances of the Ln₂NiO_4+δ - containing cells (Ln = La, Nd) is improved compared to a cell containing the classical Sr-doped LaMnO₃ (LSM) perovskite oxygen electrode showing that nickelates are promising candidates for HTSE oxygen electrodes, especially for operation below 800 °C. Indeed, current densities determined at 1.3 V are 1.1 times larger for the La₂NiO_4+δ - containing cell and 1.6 times larger for the Nd₂NiO_4+δ one compared to the LSM - containing cell at 850 °C, whereas at 750 °C they are 1.8 and 4.4 times larger, respectively. Thanks to the use of a reference electrode, by coupling impedance spectroscopy and polarization measurements, the overpotential of each working electrode is deconvoluted from the complete cell voltage under HTSE operating conditions.     

Techno-economic analysis for clean hydrogen production using solar energy under varied climate conditions

The paper discusses the feasibility of the use solar energy into hydrogen production using a photovoltaic energy system in the four main cities of Iraq. An off-grid photovoltaic system with a capacity of 22.0 kWp, an 8.0 kW alkaline electrolyser, a hydrogen compressor, and a hydrogen tank were simulated for one year in order to generate hydrogen. A mathematical model of the proposed system behavior is presented using MATLAB/Simulink, considering nine years from the 2021 to 2030 project span using hourly experimental weather data. The outcomes demonstrated that the annual hydrogen production ranged from 1713.92 kg up to 1891.12 kg, oxygen production ranged from 1199.74 to 1323.78 kg, and water consumption ranged from 7139.91 L to 7877.29 L. The hydrogen evaluated costs equal to $3.79/kg. The results show that the optimum site for solar hydrogen production systems can be established in the midwest of Iraq and in other cities with similar climates, especially those that get a lot of sunlight.     

Improved durability of SOEC stacks for high temperature electrolysis

An experimental study has been conducted at Idaho National Laboratory to demonstrate recent improvements in long-term durability of solid oxide electrolysis cells (SOEC) and stacks. Results of five stack tests are presented. Electrolyte-supported SOEC stacks were provided by Ceramatec Inc. and electrode-supported SOEC stacks were provided by Materials and Systems Research Inc. (MSRI), for these tests. Long-term durability tests were generally operated for durations of 1000 h or more. Stack tests based on technologies developed at Ceramatec and MSRI have shown significant improvement in durability in the electrolysis mode. Long-term degradation rates of 3.2%/khr and 4.6%/khr were observed for MSRI and Ceramatec stacks, respectively. One recent Ceramatec stack even showed negative degradation (performance improvement) over 1900 h of operation. Optimization of electrode and electrolyte materials, interconnect coatings, and electrolyte–electrode interface microstructures contribute to improve the durability of SOEC stacks.     

Enriched methane production using solar energy: an assessment of plant performance

A novel hybrid plant for the production of a mixture of methane and hydrogen (17 vol%) from a steam-reforming reactor whose heat duty is supplied by a concentrating solar power (CSP) plant by means of a molten salt stream is here presented.     

Hydrogen production characteristics of a bioethanol solar reforming system with solar insolation fluctuations

The development of a bioethanol steam reforming system (FBSR) is considered as a means of distributing energy using PEM fuel cells. Small-scale solar collectors (collection areas on the order of several m²) are installed in a house as a method for applying the FBSR. However, the temperature distribution of a reforming catalyst fluctuates under conditions of unstable solar insolation. Therefore, heat transfer analysis applied in reforming the catalyst layer of the reactor and the temperature distribution and transient response characteristics of the gas composition of the process were investigated. As a case study, meteorological data for representative days in March and August in Sapporo, Japan were recorded, and the hydrogen production speed, power generation output and amount of electricity purchased were analyzed. The results showed that although fluctuations in solar insolation affected the efficiency of the FBSR, the average efficiency of each representative day exceeded 40%. By installing two solar collectors, each with a collection area of 1 m², 21–25% of the average power demand of an individual house can be supplied.     

Simulation of high temperature thermal energy storage system based on coupled metal hydrides for solar driven steam power plants

Concentrating solar power plants can achieve low cost and efficient renewable electricity production if equipped with adequate thermal energy storage systems. Metal hydride based thermal energy storage systems are appealing candidates due to their demonstrated potential for very high volumetric energy densities, high exergetic efficiencies, and low costs. The feasibility and performance of a thermal energy storage system based on NaMgH₂F hydride paired with TiCr_1.6Mn_0.2 is examined, discussing its integration with a solar-driven ultra-supercritical steam power plant. The simulated storage system is based on a laboratory-scale experimental apparatus. It is analyzed using a detailed transport model accounting for the thermochemical hydrogen absorption and desorption reactions, including kinetics expressions adequate for the current metal hydride system. The results show that the proposed metal hydride pair can suitably be integrated with a high temperature steam power plant. The thermal energy storage system achieves output energy densities of 226 kWh/m³, 9 times the DOE SunShot target, with moderate temperature and pressure swings. In addition, simulations indicate that there is significant scope for performance improvement via heat-transfer enhancement strategies.     

Model development and analysis of a novel high-temperature electrolyser for gas phase electrolysis of hydrogen chloride for hydrogen production

In this study, a high temperature electrolyser for the gas phase electrolysis of hydrogen chloride for hydrogen production is proposed and assessed. A detailed electrochemical model is developed to study the J-E characteristics for the proposed electrolyser (a solid oxide electrolyser based on a proton conducting electrolyte). The developed model accounts for all major losses, namely activation, concentration and ohmic. Energy and exergy analyses are carried out, and the energy and exergy efficiencies of the proposed electrolyser are determined to be 41.1% and 39.0%, respectively. The simulation results show that at T = 1073 K, P = 100.325 kPa and J = 1000 A/m², 1.6 V is required to produce 1 mol of hydrogen. This is approximately 0.3 V less than the voltage required by a high temperature steam electrolyser (based on a proton conducting electrolyte) operating at same condition (T = 1073 K, P = 101.325 kPa and J = 1000 A/m²), suggesting that the proposed electrolyser offers a new option for high temperature electrolysis for hydrogen production, potentially with a low electrical energy requirement. The proposed electrolyser may be incorporated into thermochemical cycles for hydrogen production, like CuCl or chlorine cycles.     

Hydrogen production using biocathode single-chamber microbial electrolysis cells fed by molasses wastewater at low temperature

Molasses is by-product from sugar beet process and commonly used as raw material for ethanol production. However, the molasses wastewater possesses high level of chemical oxygen demand (COD), which needs to be properly treated before discharge. In this work, MEC technology, a promising method for hydrogen production from organic waste, was utilized to produce H₂ from molasses wastewater. In this study, the feasibility of operating the MEC at low temperatures was evaluated since the average wastewater temperature in Harbin city is lower than 10 °C. In addition, the feasibility of using biocathode as an alternative to expensive platinum (Pt) as the cathode material was also examined. Both Pt catalyzed MECs and biocathodic MECs were operated at a low temperature of 9 °C. The overall hydrogen recovery of 72.2% (E_ap = 0.6 V) was obtained when the Pt catalyst was used. In contrast, when a cheaper catalyst (biocathode; E_ap = 0.6 V) was used, hydrogen can still be produced but at a lower overall hydrogen recovery of 45.4%. This study demonstrated that hydrogen could be generation from molasses wastewater at a low temperature using a cheaper cathode material (i.e., biocathode).     

Hydrogen production from solar energy powered supercritical cycle using carbon dioxide

A hydrogen production method is proposed, which utilizes solar energy powered thermodynamic cycle using supercritical carbon dioxide (CO₂) as working fluid for the combined production of hydrogen and thermal energy. The proposed system consists of evacuated solar collectors, power generating turbine, water electrolysis, heat recovery system, and feed pump. In the present study, an experimental prototype has been designed and constructed. The performance of the cycle is tested experimentally under different weather conditions. CO₂ is efficiently converted into supercritical state in the collector, the CO₂ temperature reaches about 190 °C in summer days, and even in winter days it can reach about 80 °C. Such a high-temperature realizes the combined production of electricity and thermal energy. Different from the electrochemical hydrogen production via solar battery-based water splitting on hand, which requires the use of solar batteries with high energy requirements, the generated electricity in the supercritical cycle can be directly used to produce hydrogen gas from water. The amount of hydrogen gas produced by using the electricity generated in the supercritical cycle is about 1035 g per day using an evacuated solar collector of 100.0 m² for per family house in summer conditions, and it is about 568.0 g even in winter days. Additionally, the estimated heat recovery efficiency is about 0.62. Such a high efficiency is sufficient to illustrate the cycle performance.     

Hydrogen electrical energy storage by high-temperature steam electrolysis for next-millennium energy security

It would be highly significant if energy, which is intimately related with the continued existence of human beings, were sustainable on the basis of the present resources for the next thousand years. The effectiveness of hydrogen for energy storage by high-temperature steam electrolysis is clarified by showing its features with reference to solar energy and nuclear energy for power storage as examples. It is also shown that use of hydrogen for energy storage would be effective for widespread utilization of current energy resources, such as renewables and nuclear energy, over the next millennium.     

Hydrogen storage capacity at high pressure of raw and purified single wall carbon nanotubes produced with a solar reactor

Samples of single wall carbon nanotubes (SWNTs) were prepared using a solar reactor. Graphite targets containing different catalysts (Ni/Co, Ni/Y, Ni/Ce) allowed the synthesis of SWNTs soot in which nanotubes had different diameter distributions. Several consecutive stages of HCl treatment and thermal oxidation in air (HCl protocol) purified the samples. Another protocol involving HNO₃ treatment and H₂O₂ oxidation (HNO₃ protocol) was also used. Isotherms of hydrogen adsorption were volumetrically measured at 253 K under pressures below 6 MPa on raw and treated samples. The highest adsorption capacity (0.7  wt%) was measured on raw soot. HCl protocol clearly increases the BET surface area (_SBET)$(S_{\mathrm{BET}})$ and the microporous volume (_W0(_N2))$(W_0({\mathrm{N}}_2))$ measured by N₂ at 77 K of the treated samples with respect to the as-produced materials, whereas HNO₃ protocol decreases them. A correlation between textural properties and hydrogen storage capacities is discussed.     

Hydrogen production by biomass gasification in supercritical water using concentrated solar energy: System development and proof of concept

A novel system of hydrogen production by biomass gasification in supercritical water using concentrated solar energy has been constructed, installed and tested at the State Key Laboratory of Multiphase Flow in Power Engineering (SKLMF). The “proof of concept” tests for solar-thermal gasification of biomass in supercritical water (SCW) were successfully carried out. Biomass model compounds (glucose) and real biomass (corn meal, wheat stalk) were gasified continuously with the novel system to produce hydrogen-rich gas. The effect of direct normal solar irradiation (DNI) and catalyst on gasification of biomass was also investigated. The results showed that the maximal gasification efficiency (the mass of product gas/the mass of feedstock) in excess of 110% were reached, hydrogen fraction in the gas product also approached to 50%. The experimental results confirmed the feasibility of the system and the advantage of the process, which supports future work to address the technical issues and develop the technology of solar-thermal hydrogen production by gasification of biomass in supercritical water.