Two-step thermochemical electrolysis: An approach for green hydrogen production

Electrolysis and thermochemical water splitting are approaches to produce green hydrogen that use either an electrical potential (electrolysis) or a chemical potential (thermochemical water splitting) to split water. Electrolysis is technologically mature when applied at low temperatures, but it requires large quantities of electrical energy. In contrast to electrolysis, thermochemical water splitting uses thermal energy, as thermal energy can typically be supplied at a lower unit cost than electrical energy using concentrating solar power. Thermochemical water splitting, however, typically suffers from high thermal losses at the extremely high process temperatures required, substantially increasing the total energy required. We show how, by combining electrical and chemical potentials, a novel and cost-efficient water splitting process can be envisioned that overcomes some of the challenges faced by conventional electrolysis and thermochemical water splitting. It uses a mixed ionic and electronic conducting perovskite with temperature-dependent oxygen non-stoichiometry as an anode in an electrolyzer. If solar energy is used as the primary source of all energy required in the process, the cost of the energy required to produce hydrogen could be lower than in high-temperature electrolysis by up to 7%.     

Dynamic analyses of regenerative fuel cell power for potential use in renewable residential applications

A model of a solar-hydrogen powered residence, in both stand-alone and grid parallel configurations, was developed using Matlab/Simulink^®$\mathrm{Matlab}/{\mathrm{Simulink}}^{\circledR }$. The model assesses the viability of employing a regenerative fuel cell (RFC) as an energy storage device to be used with photovoltaic (PV) electrical generation. Other modes of energy storage such as batteries and hybrid storage were also evaluated. Analyses of various operating conditions, system configurations, and control strategies were performed. Design requirements investigated included RFC sizing, battery sizing, charge/discharge rates, and state of charge limitations. Dynamic load demand was found to be challenging to meet, requiring RFC and or battery sizes significantly larger than those required to meet average power demand. Employing a RFC with batteries in a hybrid configuration increased PV utilization and both battery efficiency and power density. Grid parallel configurations were found to alleviate many of the difficulties associated with energy storage costs and meeting peak demand.     

Prospects and challenges for green hydrogen production and utilization in the Philippines

The Philippines is exploring different alternative sources of energy to make the country less dependent on imported fossil fuels and to reduce significantly the country's CO₂ emissions. Given the abundance of renewable energy potential in the country, green hydrogen from renewables is a promising fuel because it can be utilized as an energy carrier and can provide a source of clean and sustainable energy with no emissions. This paper aims to review the prospects and challenges for the potential use of green hydrogen in several production and utilization pathways in the Philippines. The study identified green hydrogen production routes from available renewable energy sources in the country, including geothermal, hydropower, wind, solar, biomass, and ocean. Opportunities for several utilization pathways include transportation, industry, utility, and energy storage. From the analysis, this study proposes a roadmap for a green hydrogen economy in the country by 2050, divided into three phases: I–green hydrogen as industrial feedstock, II–green hydrogen as fuel cell technology, and III–commercialization of green hydrogen. On the other hand, the analysis identified several challenges, including technical, economic, and social aspects, as well as the corresponding policy implications for the realization of a green hydrogen economy that can be applied in the Philippines and other developing countries.     

Role and prospects of green quantum dots in photoelectrochemical hydrogen generation: A review

Eco-friendly quantum dots (QDs) can be termed green QDs which stand as an attractive choice to modify the properties of known semiconductors in the direction of getting efficient photoelectrodes for solar-induced photoelectrochemical (PEC) splitting of water, due to their peculiar properties. Thus, it is of high significance to analyze their merit/demerit as an effective scaffold in PEC cell. QDs are known for their excellent optical properties however, the coupling of green QDs with semiconductor is not only useful in improving absorption characteristics but also promotes charge transfer. This review has undertaken the critical analysis on the worldwide research going on the green QDs modified photoelectrode with respect to their optical, electrical & photoelectrochemical properties, role, usefulness, efficiency, and finally the success in PEC system for hydrogen production. Various methods on the facile synthesis & sensitization techniques of green QDs available in the literature have also been discussed. Further, recent advances on the development of green QDs based photo-electrode, along with major challenges of using green QDs in this field have also been presented.     

Charge/discharge and cycling performance of flexible carbon paper electrodes in a regenerative hydrogen/vanadium fuel cell

The regenerative hydrogen/vanadium fuel cell (RHVFC) is investigated with Freudenberg carbon paper electrodes (CPs). Along with thermal treatment, the Freudenberg CPs are also treated with reduced graphene oxide (rGO) using electrophoretic deposition at 300 V. The rGO modified CP results in 25% higher power density than its untreated counterpart under the same operating conditions. In comparison to the first preliminary study, the power density reported herein is more than four times higher. Additionally, the Freudenberg CPs modified with heat treatment followed by rGO deposition facing the membrane (rGOHTFM) provide the best electrolyte discharge utilization (UE) of 99%, followed by untreated (98%) and heat treated samples (97%) at 50 mA cm⁻². The rGOHTFM also record high charge and discharge energy efficiencies (η_E) of 93% at the same current density, which is slightly higher than untreated CPs (η_E = 91%). Cycling the system 10 times also results in higher η_E and UE for rGOHTFM CP (η_E = 92% and UE = 99% on average) in comparison to untreated electrodes (η_E = 86% and UE = 97% on average). In comparison the widely investigated SGL 10AA CP has lower efficiencies and utilization as expected (η_E = 74% and UE = 83% on average).     

Model validation and performance analysis of regenerative solid oxide cells: Electrolytic operation

The use of regenerative, high temperature solid oxide cells (SOCs) as energy storage devices has the potential for round-trip efficiencies that are competitive with other storage technologies. The focus of the current study is to investigate regenerative SOC operation (i.e., working in both fuel cell and electrolysis modes) through a combination of modeling and numerical simulation. As an intermediate step, this paper focuses on the electrolysis mode and presents a dynamic cell model that couples the reversible electrochemistry, reactant chemistry, and the thermo-fluidic phenomena inside a cell channel. The model is calibrated and validated using available experimental and numerical data for button cells, single cells, and multi-cell stacks supplied with either steam or syngas. Parametric studies are also performed to show how the investigated parameters affect model validity. The results show that the present model can accurately simulate the electrolytic cell behavior, especially in the low current range, which is a favored operating point in practical systems. It is observed that improvements in stack-level model precision require further investigation to better represent the contact resistance of the stack components and to improve the estimation of the activation polarization throughout the operating envelope. It is also concluded that the CO₂ electrochemical reaction can be neglected when the concentration of the steam supplied to the cell is high enough to support the water–gas shift reaction.     

Optimization of self-regulated hydrogen production from photovoltaic energy

The use of photovoltaic energy (PV) for the production of hydrogen by using autonomous modular self-regulated systems is studied. Results are compared with those obtained for controlled systems. It was proved that for small and low-cost applications, it is possible to eliminate any control system with yields as high as 91.2% in the PV-electrolyzer interface for a sunny day. Self-regulated systems are thus an excellent, safe, cheap and environmentally friendly alternative for applications in isolated sites, especially in emerging countries.     

Generation of high-pressure hydrogen for fuel cell electric vehicles using photovoltaic-powered water electrolysis

Increasing the utilization of electric drive systems including hybrid, battery, and fuel cell electric vehicles (FCEV) will reduce the usage of petroleum and the emission of air pollution by vehicles. The eventual production of electricity and hydrogen in a renewable fashion, such as using solar energy, can achieve the long-term vision of having no tailpipe emissions, as well as eliminating the dependence of the transportation sector on dwindling supplies of petroleum for its energy. Before FCEVs can be introduced in large numbers, a hydrogen-fueling infrastructure is needed. This report describes an early proof-of-concept for a distributed hydrogen fueling option in which renewably generated, high-pressure hydrogen is dispensed at an FCEV owner’s home. In an earlier report we described the design and initial characterization of a solar photovoltaic (PV) powered electrolyzer/storage/dispensing (ESD) system that was a proof-of-concept for a single FCEV home fueling system. In the present report we determined the efficiency and other operational characteristics of that PV-ESD system during testing over a 109-day period at the GM Proving Ground in Milford, MI, at a hydrogen output pressure of approximately 2000 psi (13.8 MPa). The high pressure was achieved without any mechanical compression via electrolysis. Over the study period the photovoltaic solar to electrical efficiency averaged 13.7%, the electrolyzer efficiency averaged 59%, and the system solar to hydrogen efficiency averaged 8.2% based on the hydrogen lower heating value. A well-documented model used to evaluate solar photovoltaic power systems was used to calculate the maximum power point values of the voltage, current, and power of our PV system in order to derive the coupling factor between the PV and ESD systems and to determine its behavior over the range of environmental conditions experienced during the study. The average coupling factor was near unity, indicating that the two systems remained coupled in an optimal fashion. Also, the system operated well over a wide range of meteorological conditions, and in particular it responded quickly to instantaneous changes in the solar irradiance (caused by clouds) with negligible effect on the overall efficiency. During the study up to 0.67 kg of high-pressure hydrogen was generated on a sunny day for fueling FCEV. Future generations of high-pressure electrolyzers, properly combined with solar PV systems, can offer a compact, efficient, and environmentally acceptable system for FCEV home fueling.     

Fault detection and diagnosis methods for green hydrogen production: A review

One of the green hydrogen projects is Zero Emission Hydrogen Turbine Center (ZEHTC), in which solar panels, PEM electrolyzer, and diaphragm compressor are used to generate power, produce hydrogen and store hydrogen at high pressure, respectively. Faults in any components of photovoltaic (PV) systems, PEM electrolyzers, and diaphragm compressors can seriously affect the efficiency, energy yield as well as security, and reliability of the entire system, if not detected and corrected quickly. In this paper, the types and causes of PV systems, PEM electrolyzer, and diaphragm compressors failures are presented, then different methods proposed in the literature for fault detection and diagnosis (FDD) of systems are reviewed and discussed. Special attention is paid to methods that can accurately detect, localize and classify possible faults occurring in a PV arrays. The advantages and limits of FDD methods in terms of feasibility, complexity, cost-effectiveness and generalization capability for large-scale integration are highlighted. Based on the reviewed papers, challenges and recommendations for future research direction are also provided. In this work different model-based approaches are investigated as well as their validation and applications. An overview of different methodologies available in the literature is proposed, which is oriented to help in developing suitable diagnostic tool for PEM electrolyzer monitoring and fault detection and isolation (FDI). Model-based methods provide fault detection and identification, are easy to implement, and could be conducted during system operation.     

Opportunities for green hydrogen production in petroleum refining and ammonia synthesis industries in India

Increasing penetration of renewable electricity in the power systems coupled with reduction in its cost has resulted in increased interest in green hydrogen globally. Industry has been using fossil fuel-based hydrogen as an input for several decades. This paper makes an assessment of existing hydrogen production capacities in petroleum refineries and ammonia synthesis units in India along with estimating the potential for installing solar photovoltaic (SPV) powered alkaline electrolysers for producing green hydrogen and SPV capacity required for this purpose. Levelised cost of hydrogen production in these industries in India has been analysed and found to be competitive. The paper also discusses about water requirement, land requirement for SPV power plants, CO₂ emissions avoided and likely investment to be made for establishing infrastructure for green hydrogen production. With launching of national hydrogen mission in India, a transition to green hydrogen by the industry appears to be a near term possibility.     

Techno-economic assessment of green hydrogen and ammonia production from wind and solar energy in Iran

This paper presents a comprehensive technical and economic assessment of potential green hydrogen and ammonia production plants in different locations in Iran with strong wind and solar resources. The study was organized in five steps. First, regarding the wind density and solar PV potential data, three locations in Iran were chosen with the highest wind power, solar radiation, and a combination of both wind/solar energy. All these locations are inland spots, but since the produced ammonia is planned to be exported, it must be transported to the export harbor in the South of Iran. For comparison, a base case was also considered next to the export harbor with normal solar and wind potential, but no distance from the export harbor. In the second step, a similar large-scale hydrogen production facility with proton exchange membrane electrolyzers was modeled for all these locations using the HOMER Pro simulation platform. In the next step, the produced hydrogen and the nitrogen obtained from an air separation unit are supplied to a Haber-Bosch process to synthesize ammonia as a hydrogen carrier. Since water electrolysis requires a considerable amount of water with specific quality and because Iran suffers from water scarcity, this paper, unlike many similar research studies, addresses the challenges associated with the water supply system in the hydrogen production process. In this regard, in the fourth step of this study, it is assumed that seawater from the nearest sea is treated in a desalination plant and sent to the site locations. Finally, since this study intends to evaluate the possibility of green hydrogen export from Iran, a detailed piping model for the transportation of water, hydrogen, and ammonia from/to the production site and the export harbor is created in the last step, which considers the real routs using satellite images, and takes into account all pump/compression stations required to transport these media. This study provides a realistic cost of green hydrogen/ammonia production in Iran, which is ready to be exported, considering all related processes involved in the hydrogen supply chain.     

Modelling and control of hydrogen and energy flows in a network of green hydrogen refuelling stations powered by mixed renewable energy systems

The planning of a hydrogen infrastructure with production facilities, distribution chains, and refuelling stations is a hard task. Difficulties may rise essentially in the choice of the optimal configurations. An innovative design of hydrogen network has been proposed in this paper. It consists of a network of green hydrogen refuelling stations (GHRSs) and several production nodes. The proposed model has been formulated as a mathematical programming, where the main decisions are the selection of GHRSs that are powered by the production nodes based on distance and population density criteria, as well the energy and hydrogen flows exchanged among the system components from the production nodes to the demand points. The approaches and methodologies developed can be taken as a support to decision makers, stakeholders and local authorities in the implementation of new hydrogen infrastructures. Optimal configurations have been reported taking into account the presence of an additional hydrogen industrial market demand and a connection with the electrical network. The main challenge that has been treated within the paper is the technical feasibility of the hydrogen supply chain, that is mainly driven by uncertain, but clean solar and wind energy resources. Using a Northern Italian case study, the clean hydrogen produced can be technically considered feasible to supply a network of hydrogen refuelling stations. Results show that the demands are satisfied for each time period and for the market penetration scenarios adopted.     

Gas transport in hydrogen electrode of solid oxide regenerative fuel cells for power generation and hydrogen production

To further develop solid oxide regenerative fuel cell (SORFC) technology, the effect of gas diffusion in the hydrogen electrode on the performance of solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) is investigated. The hydrogen electrode-supported cells are fabricated and tested under various operating conditions in both the power generation and hydrogen production modes. A transport model based on the dusty-gas model is developed to analyze the multi-component diffusion process in the porous media, and the transport parameters are obtained by applying the experimentally measured limiting current data to the model. The structural parameters of the porous electrode, such as porosity and tortuosity, are derived using the Chapman–Enskogg model and microstructural image analysis. The performance of an SOEC is strongly influenced by the gas diffusion limitation at the hydrogen electrode, and the limiting current density of an SOEC is substantially lower than that of an SOFC for the standard cell structure under normal operating conditions. The pore structure of the hydrogen electrode is optimized by using poly(methyl methacrylate) (PMMA), a pore-forming agent, and consequently, the hydrogen production rate of the SOEC is improved by a factor of greater than two under moderate humidity conditions.     

Model predictive control of an on-site green hydrogen production and refuelling station

The expected increase of hydrogen fuel cell vehicles has motivated the emergence of a significant number of studies on Hydrogen Refuelling Stations (HRS). Some of the main HRS topics are sizing, location, design optimization, and optimal operation. On-site green HRS, where hydrogen is produced locally from green renewable energy sources, have received special attention due to their contribution to decarbonization. This kind of HRS are complex systems whose hydraulic and electric linked topologies include renewable energy sources, electrolyzers, buffer hydrogen tanks, compressors and batteries, among other components. This paper develops a linear model of a real on-site green HRS that is set to be built in Zaragoza, Spain. This plant can produce hydrogen either from solar energy or from the utility grid and is designed for three different types of services: light-duty and heavy-duty fuel cell vehicles and gas containers. In the literature, there is a lack of online control solutions developed for HRS, even more in the form of optimal online control. Hence, for the HRS operation, a Model Predictive Controller (MPC) is designed to solve a weighted multi-objective online optimization problem taking into account the plant dynamics and constraints as well as the disturbances prediction. Performance is analysed throughout 210 individual month-long simulations and the effect of the multi-objective weighting, prediction horizon, and hydrogen selling price is discussed. With the simulation results, this work shows the suitability of MPC for HRS control and its significant economic advantage compared to the rule-based control solution. In all simulations, the MPC operation fulfils all required services. Moreover, results show that a seven-day prediction horizon can improve profits by 57% relative to a one-day prediction horizon; that the battery is under-sized; or that the MPC operation strategy is more resolutive for low hydrogen selling prices.     

Opportunities and challenges for thermally driven hydrogen production using reverse electrodialysis system

Ongoing and emerging renewable energy technologies mainly produce electric energy and intermittent power. As the energy economy relies on banking energy, there is a rising need for chemically stored energy. We propose heat driven reverse electrodialysis (RED) technology with ammonium bicarbonate (AmB) as salt for producing hydrogen. The study provides the authors’ perspective on the commercial feasibility of AmB RED for low grade waste heat (333 K–413 K) to electricity conversion system. This is to our best of knowledge the only existing study to evaluate levelized cost of energy of a RED system for hydrogen production. The economic assessment includes a parametric study, and a scenario analysis of AmB RED system for hydrogen production. The impact of various parameters including membrane cost, membrane lifetime, cost of heating, inter-membrane distance and residence time are studied. The results from the economic study suggests, RED system with membrane cost less than 2.86 €/m², membrane life more than 7 years and a production rate of 1.19 mol/m²/h or more are necessary for RED to be economically competitive with the current renewable technologies for hydrogen production. Further, salt solubility, residence time and inter-membrane distance were found to have impact on levelized cost of hydrogen, LCH. In the present state, use of ammonium bicarbonate in RED system for hydrogen production is uneconomical. This may be attributed to high membrane cost, low (0.72 mol/m²/h) hydrogen production rate and large (1,281,436 m²) membrane area requirements. There are three scenarios presented the present scenario, market scenario and future scenario. From the scenario analysis, it is clear that membrane cost and membrane life in present scenario controls the levelized cost of hydrogen. In market scenario and future scenario the hydrogen production rate (which depends on membrane properties, inter-membrane distance etc.), the cost of regeneration system and the cost of heating controls the levelized cost of hydrogen. For a thermally driven RED system to be economically feasible, the membrane cost not more than 20 €/m²; hydrogen production rate of 3.7 mol/m²/h or higher and cost of heating not more than 0.03 €/kWh for low grade waste heat to hydrogen production.     

Electrochemical hydrogen storage: Opportunities for fuel storage,batteries, fuel cells,and supercapacitors

Solid-state storage of hydrogen is a possible breakthrough to realise the unique futures of hydrogen as a green fuel. Among possible methods, electrochemical hydrogen storage is very promising, as can be conducted at low temperature and pressure with a simple device reversibly. However, it has been overshadowed by the physical hydrogen storage in the literature, and thus, research efforts are not adequately connected to lead us in the right direction. On the other hand, electrochemical hydrogen storage is the basis of some other electrochemical power sources such as batteries, fuel cells, and supercapacitors. For instance, available hydrogen storage materials can build supercapacitors with exceptionally high specific capacitance in order of 4000 F g^?1. In general, electrochemical hydrogen storage plays a substantial role in the future of not only hydrogen storage but also electrochemical power sources. There are some vague points which have obscured our understanding of the corresponding system to be developed practically. This review aims to portray the entire field and detect those ambiguous points which are indeed the key obstacles. It is clarified that different materials have somehow similar mechanisms for electrochemical hydrogen storage, which is initiated by hydrogen dissociation, surface adsorption and probably diffusing deep within the bulk material. This mechanism is different from the insertion/extraction of alkali metals, though battery materials look similar. Based on the available reports, it seems that the most promising material design for the future of electrochemical hydrogen storage is a class of subtly designed nanocomposites of Mg-based alloys and mesoporous carbons.     

A review of unitized regenerative fuel cell stack: Material,design and research achievements

The stack design of a unitized regenerative fuel cell (URFC) can modify the structure of cells that can be used as storage and energy regenerator aside from cells that use other sources such as solar or wind energy. A reversible unitized polymer electrolyte membrane fuel cell (PEMFC) contains a dual-functional single cell that is less expensive and has enhanced performance. The use of URFCs on hydrogen and oxygen is preferred because it is highly efficient, environmentally friendly, and uses power generators. The stack, then, must be made affordable or accessible. The expenses of URFC stack must be reduced by improving its design, materials, and performance. This study referred to recent studies on developing a method to cut the expenses of the URFC stack. The study also aims to determine its main constituents and to look further into its design by observing its performance and electrochemical behaviors. It also presents the issues that are currently encountered in this field.     

A methodology of computation,design and optimization of solar Stirling power plant using hydrogen/oxygen fuel cells

The objective of this paper is to develop a methodology to determine how many houses could be fueled from the solar energy captured by a number of solar Stirling modules (with a fixed dish area per module) and also to determine the minimum necessary area of the fuel cell to ensure the amount of power needed to meet daily energy use requirements. The detailed method includes the effect of the fuel cell efficiency function on the power consumption of the user. Experimental data from our laboratory are used to determine the fuel cell efficiency as a function of the electric current density for a specific power demand. As an illustrative example, the analysis is applied to a residential area having a specific electrical demand. Using the developed method, the number of houses that could be fueled directly by the stored hydrogen is determined, and also the minim fuel cell area required.