Solar-Powered Water Electrolysis Using Hybrid Solid Oxide Electrolyzer Cell (SOEC) for Green Hydrogen—A Review

Solid Oxide Electrolysis Cells (SOECs) are advancing toward global commercialization, driven by significant improvements in cell performance, extended lifetimes, and effective applications. Leading companies like Bloom Energy and Topsoe are demonstrating the feasibility of industrial-scale SOECs hydrogen production and synthetic fuel generation. Additionally, SOECs are being integrated with renewable energy and industrial heat sources to reduce green hydrogen cost and improving energy efficiency. Despite challenges like degradation and expensive costs, ongoing research are paving the way for SOECs to play a pivotal role in the global energy transition.China has been actively involved in the SOECs development since the early stages of this technology. However, the Chinese SOEC industry has not yet reached the same level of maturity as its international counterparts. Currently, SOEC technology in China remains in the research and small-scale demonstration phase, hindered by challenges such as expensive capital costs, poor lifespan, and unclear applications. Despite these barriers, China boasts the world's largest green hydrogen market, where alkaline electrolyzers (AECs) currently dominate due to their lower costs. However, SOECs known for their superior efficiency, have good potential application prospects in the future if key bottlenecks such as cost, and durability can be effectively addressed. This transition could significantly enhance global green hydrogen production capabilities and contribute to decarbonization goals.The primary objectives for the Chinese SOEC industry are: (1) enhancing durability, and (2) reducing hydrogen production costs. To achieve these goals, specific efforts are being directed at three key areas: (1) Material and cell: develop advancing surface defect theory and novel cell (micro-)structures to achieve higher current densities at lower temperatures; (2) Stack: design advanced stack structures and improve manufacturing procedures to enhance stack consistency, reliability, robustness, and performance; (3) System: develop cost-effective BoPs, enable high-value chemical production via effective integration. These targeted initiatives aim to address critical challenges and position the Chinese SOEC industry as a global leader in green hydrogen area. SOEC development is vital for building a green energy and chemical industry and promoting China's energy structure transformation.

With the development of globalization and public increase awareness of the greenhouse effect, and there are strategic objectives of peak carbon emission and carbon neutrality that are realized, building a clean, low-carbon, safe, and efficient new energy system has become a consensus in the global world. Under this background, hydrogen, with its clean, zero-carbon emissions (especially carbon dioxide, which contribute to the greenhouse) and high energy density far exceeding that of traditional energy sources, is widely viewed as a key strategic alternative energy source that leads the future energy revolution. Among the numerous hydrogen production technologies, water electrolysis, particularly the "green hydrogen" production route that deeply integrates with fluctuating renewable energy sources such as wind, photovoltaics, and some other, is highly attractive because it can effectively address the storage and absorption issues of renewable energy. It is recognized as one of the core pillar technologies for achieving deep decarbonization and achieving green transformation of the energy system. Among the different routes for hydrogen production (through compare with the alkaline membrane electrolysis and the solid oxide electrolysis cell, later AWE and SOCE will be used respectively to refer to), water electrolysis is an attractive process for integration with renewable sources of energy like wind and photovoltaics and is considered one of the key technologies to allow a green transition of energy systems. Proton exchange membrane electrolysis (PEM) technology has attracted much attention from the academia and industry in the previous years because of its significant advantages, including a large current density, high dynamic response speed, high hydrogen purity, and direct production of high-pressure hydrogen, which is more fitted to the active and unstable renewable energy. Nevertheless, the development of this technology is still hindered by precious-metal reliance, high cost, and low durability. This paper is expected to offer theoretical reference and technical support for the large-scale applications and the industrialization of PEM water electrolysis for hydrogen production, by systematically analyzing the research work of material optimization, process improvement, and system integration.

The production of hydrogen through water electrolysis has emerged as a promising alternative to decarbonizing the energy sector, especially when integrated with renewable energy sources. Among the key operational parameters that affect electrolysis performance, temperature and current density play a critical role in determining the energy efficiency, hydrogen yield and durability of the system. The study presents a Systematic Literature Review (SLR) that includes peer-reviewed publications from 2018 to 2025, focusing on the effects of temperature and current density across a variety of electrolysis technologies, including alkaline (AEL), proton exchange membrane (PEMEL), and solid oxide electrolysis cells (SOEC). A total of seven high-quality studies were selected following the PRISMA 2020 framework. The results show that high temperatures improve electrochemical kinetics and reduce excess potential, especially in PEM and SOEC systems, but can also accelerate component degradation. Higher current densities increase hydrogen production rates but lead to lower Faradaic efficiency and increased material stress. The optimal operating range was identified for each type of electrolysis, with PEMEL performing best at 60–80 °C and 500–1000 mA/cm2, and SOEC at >750 °C. In addition, system-level studies emphasize the importance of integrating hydrogen production with flexible generation and storage infrastructure. The review highlights several research gaps, including the need for dynamic modeling, multi-parameter control strategies, and techno-economic assessments. These findings provide a basic understanding for optimizing hydrogen electrolysis systems in low-carbon energy architectures.

Hydrogen energy has been hailed as a versatile energy of the future that could aid the transition to net-zero emissions. It has large potential as an alternate fuel source for mobility and power, heating and feedstock for the industry. The energy carrier is produced from water electrolysis technology using different types of electrolyzer (i.e., Proton Exchange Membrane (PEM) or Solid Oxide Electrolysis Cells (SOECs)) for hydrogen separation process. In this energy research journey, PETRONAS has jointly worked with SLB to evaluate the feasibility of using SOECs for green hydrogen production. The study's focus is to explore integrating SOECs into existing industrial facilities creating hybrid systems, specifically with available flue gas from combustion process e.g. power generation. This allows for the utilization of waste heat from existing processes to enhance overall energy efficiency in hydrogen production. To understand hydrogen production and its utilization in the existing facility, the full system including existing gas turbines, solid oxide electrolyzer cells (SOECs), a hydrogen compression train, and a temperate cooling water system were modeled in a process simulation software. The model also included a heat recovery steam generator (HRSG) to recover the energy from gas turbine exhaust gases to heat water feed to produce saturated steam which will be the feed to SOEC. Several configurations considering heat integrations were explored, including heat recovery from SOEC product stream. Various sensitivities were run for different configurations of the process to study hydrogen purity, hydrogen blending, overall power required, water required in the overall process, and power produced by the hydrogen generated from SOEC and CO2 emission values in all the configuration. The results were compared and evaluated to help assess how variation in parameters affect the performance or outcome. The results were evaluated for blending the produced hydrogen with the existing export gas before and after export gas compression and how it influences the hydrogen purity. Hydrogen blending with the fuel gas to the gas turbine also helped in overall reduction of CO2 emission. It was observed that additional cooling of the hydrogen stream to achieve better hydrogen purity did not significantly help in reducing CO2 emissions when hydrogen is used as fuel gas; therefore, cooling with temperate water system can be considered. All the cases were compared and evaluated for expanding the application of green hydrogen technologies in the facility considering viability and reduction in emissions. The study was a part of a collaborative research initiative by the industry players to accelerate the development and deployment of SOEC technologies in existing facilities. The results from the study provided an overall understanding of adding SOEC in the facility and valuable insights to the stakeholders to make well-informed choices on the configuration.

Due to the random fluctuations in power experienced by high-temperature green electric hydrogen production systems, further deterioration of spatial distribution characteristics such as temperature, voltage/current, and material concentration inside the solid oxide electrolysis cell (SOEC) stack may occur. This has a negative impact on the system’s flexibility and the corresponding control capabilities. In this paper, based on the SOEC electrolytic cell model, a comprehensive optimization method using an adaptive incremental Kriging surrogate model is proposed. The reliability of this method is verified by accurately analyzing the dynamic performance of the SOEC and the spatial characteristics of various physical quantities. Additionally, a thermal dynamic analysis is performed on the SOEC, and an adaptive time-varying LPV-MPC optimization control method is established to ensure the temperature stability of the electrolysis cell stack, aiming to maintain a stable, efficient, and sustainable SOEC operation. The simulation analysis of SOEC hydrogen production adopting a variable load operation has demonstrated the advantages of this method over conventional PID control in stabilizing the temperature of the stack. It allows for a rapid adjustment in the electrolysis voltage and current and improves electrolysis efficiency. The results highlighted that the increase in the electrolysis load increases the current density, while the water vapor, electrolysis voltage, and H2 flow rate significantly decrease. Finally, the SOEC electrolytic hydrogen production module is introduced for optimization scheduling of energy consumption in Xinjiang, China. The findings not only confirmed that the SOEC can transition to the current load operating point at each scheduling period but also demonstrated higher effectiveness in stabilizing the stack temperature and improving electrolysis efficiency.

As the world progresses toward a sustainable energy future, green hydrogen emerges as an innovative solution in the global effort to achieve decarbonization. This study examines the performance of a photovoltaic (PV)-driven solid oxide electrolyzer cell (SOEC) in producing green hydrogen under dynamic and unpredictable solar energy conditions. High-temperature electrolyzers provide substantial advantages in conversion efficiency compared to their low-temperature counterparts. The study focuses on designing and analyzing the thermodynamic and electrochemical performance of an SOEC capable of generating hydrogen and oxygen from water using solar energy. The SOEC was evaluated in exothermic and endothermic modes to ensure autonomous operation without external heat sources. The heat exchanger network was optimized to enhance system performance. This approach equips the SOEC system to adapt to renewable hydrogen production, particularly within a PV system configuration. The PV system was analyzed using two modes: direct and indirect coupling. A parametric study explores the impacts of key operating conditions, such as temperature, pressure, and current density, on cell potential and overall performance. The SOEC achieved energy and exergy efficiencies of 88% and 78%, respectively. A PV system comprising eight panels in series and seven panels in parallel generates 27.72 kW of power directly supplied to the electrolyzer. With a total annual solar energy radiation of 2.36 MWh/m2, the electrolyzer produces approximately 1500 kg of hydrogen and 12 000 kg of oxygen while consuming 13 500 kg of water annually. The findings of this study highlight significant advancements in the efficiency and stability of PV-driven SOEC.

Through the carbon combustion process, the oxygen produced by solid oxide electrolysis cell (SOEC) in the purging gas can be consumed. And the purging gas with low oxygen partial pressure can be recycled into the anode of SOEC, which achieves ultra-low power consumption for hydrogen production. In this study, the I-V curve of steam electrolysis in SOEC with CO2 anode gas is analyzed and discussed. The results show that the cell voltage for hydrogen production can be reduced to 0.62 V at 400 mA/cm2 under CO2 atmosphere. A combined process coupled with carbon fuel combustion and SOEC hydrogen production is proposed. By comparing three different processes of single SOEC, SOEC with heat supply directly by combustion and SOEC coupled with combustion, the advantages of SOEC hydrogen production coupled with carbon fuel combustion are analyzed. The results show that the ultra-low power consumption of SOEC can be achieved by matching the anode circulating gas flow rate, carbon fuel usage and external oxygen amount. When considering the energy efficiency of electricity to hydrogen, carbon fuel combustion can significantly reduce the electrolysis voltage and improve the energy efficiency of the system, but it will lead to an increase in the amount of anode circulating gas.

Comparative Life-Cycle-Assessment analysis of three major water electrolysis technologies while applying various energy scenarios for a greener hydrogen production

With the rapid development of hydrogen production technology by using solar energy, the research of Solid Oxide Electrolysis Cell (SOEC) and Photovoltaic/Thermal (PV/T) system have become popular. A design scheme of hydrogen production system based on PV/T technology was proposed. The electrolytic cell combined photovoltaic panels, trough solar collectors and multiple heat exchagers to improve the overall efficiency of the hydrogen production system. The efficiency was predicted based on empirical models. The results showed that the hydrogen production efficiency of SOEC increased with increasing temperature and with decreasing current density. However, the balance between energy efficiency and hydrogen production rate of SOEC needed to be taken into account. The predicted hydrogen production efficiency of SOEC and overall system efficiency also agreed well with the results available in literature.

Control strategy of solid oxide electrolysis cell operating temperature under real fluctuating renewable power

Chapter 3 - Hydrogen Production From Water Electrolysis

The global consensus holds that water electrolysis from renewable energy sources is the primary source of lowcarbon hydrogen supply in the future. Solid oxide electrolyzer cell (SOEC) with high efficiency, simple structure, flexible operation, and environmental friendliness has become a hot topic in green hydrogen research. This paper focuses on the thermal balance characteristics of the SOEC. An efficiency-power model that considers the thermal balance of the SOEC system with renewable energy sources is established. Then, the optimization method of SOEC operation by controlling the electrolysis current and water flow is proposed to maximize operating profit. The proposed model and method are verified by an example of wind plant data in the Gonghe basin of Qinghai Province. Moreover, the optimal electrolysis current and water mass flow values under the SOEC economic operation strategy are analyzed. The results show that the operation optimization method obtained by considering the thermal balance characteristic of the SOEC efficiency-power model can ensure the economical of SOEC while flexibly controlling the efficiency, which provides a helpful reference for the economic operation strategy of SOEC in practical engineering.

The intensification technologies to water electrolysis for hydrogen production – A review

Molecular hydrogen (H2) is a vital next-generation energy carrier, due to its high energy density, universal abundance, and ability to produce electricity in a fuel cell without greenhouse gas emissions. Critical to the adoption of hydrogen energy is the ability to produce H2 cleanly via the electrolysis of water. Solid oxide electrolyzer cells (SOECs) are attractive technologies to achieve this goal, as they can use excess thermal energy or other renewable energy sources to convert water into H2. However, the fundamental physics that determines the performance of SOECs—including sources of performance loss and degradation—is relatively poorly understood.Here, we describe first-principles calculations based on hybrid density functional theory (DFT) aimed at studying efficiency loss in proton-conducting SOECs based on the oxide electrolytes BaZrO3 (BZO) and BaCeO3 (BCO). These materials are acceptor-doped with a trivalent element such as yttrium to introduce protons; however, such doping can also increase electrical leakage in devices, which limits their Faradaic efficiency. Our calculations describe the properties of localized polarons in BZO and BCO: hole polarons form favorably in both materials, while electron polarons are only stabile in BCO and in Ce-containing alloys. Under typical operating conditions, large concentrations of hole polarons may be present; therefore, to limit the risk of p-type electrical leakage, it is advantageous to avoid extreme oxygen-rich conditions and high dopant concentrations [1].High ionic conductivity also requires large proton concentrations. We examine avenues to achieve this requirement by calculating the formation energy of protons and their concentrations under various conditions. Proton concentrations will be highest under wet conditions, with oxygen vacancies becoming more dominant under drier conditions. Encouragingly, higher protonation levels correlate with lower concentrations of hole polarons, implying lower electrical leakage with higher hydration levels. In addition to traditional protonation pathways, we also explore a novel hydrogenation mechanism via hydroxyl incorporation, which does not require acceptor doping. However, this process is unfavorable except under extremely wet conditions [2].These results provide crucial insights for understanding the complex behavior of these materials in situ. Determining how to promote ionic conductivity at the expense of electrical leakage is critical to optimizing their performance in SOECs and related devices.This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.[1] A. J. E. Rowberg, M. Li, T. Ogitsu, J. B. Varley, Phys. Rev. Mater. 7, 015402 (2023).[2] A. J. E. Rowberg, M. Li, T. Ogitsu, J. B. Varley, Mater. Adv. 4, 6233-6243 (2023).

A novel system for the production of pure hydrogen from natural gas based on solid oxide fuel cell–solid oxide electrolyzer