单体固体氧化物电解池极化损失分析及阴极微结构优化

基于高温固体氧化物电解池(SOEC)的高温蒸汽电解(HTSE)制氢技术作为一种非常有前景的大规模核能制氢新方法, 受到国际上的迅速关注. 但如何控制电解模式下的极化能量损失和性能衰减是HTSE实用化的关键. 本文通过在线电化学阻抗测试技术, 研究了实际运行状态下的单体固体氧化物池(SOC)在电池模式和电解模式下的极化阻抗分布, 阐述了SOEC与高温固体氧化物燃料电池(SOFC)的差异, 确定了SOEC氢电极支撑层水蒸气扩散过程极化损失大是制约电解池制氢性能提高的主要因素. 在此基础上, 采用聚甲基丙烯酸甲酯(PMMA)造孔剂对氢电极支撑层的微观结构进行了调整和优化. 微结构优化后, 氢电极材料的孔隙率提高了50%, 孔隙为规则圆形, 分布均匀, 更利于气体扩散; 电解电压1.3 V时, 单位面积产氢率高达328.1 mL·cm^-2·h^-1(标准态), 为改进前电解池的2倍, 实现50 h以上连续稳定性运行. 研究成果可为HTSE的实际应用提供一定的理论数据和技术基础.     

高温固体氧化物电解池钙钛矿型氧电极材料Ba_xSr_(1-x)Co_(0.8)Fe_(0.2)O_(3-δ)结构计算与性能研究

研究和开发高性能的钙钛矿型混合电导氧化物是目前高温固体氧化物电解池(SOEC)氧电极材料研究的热点.选择BaxSr1-xCo0.8Fe0.2O3-δ系列材料,通过对材料的容差因子、关口半径、晶格自由体积等计算,以及对平均键能、B位离子的变价能力、催化活性等方面的分析,确定了A位最佳配比.对优化出的Ba0.5Sr0.5Co0.8Fe0.2O3-δ材料的电化学性能进行了研究,并与自制的La0.2Sr0.8MnO3(LSM)氧电极材料进行了比较.结果表明:850℃下阳极极化阻抗(ASR)仅为0.07Ωcm2,远低于LSM;将其应用于SOEC氧电极进行高温电解制氢试验,产氢速率为相同条件下LSM的2.3倍,说明将Ba0.5Sr0.5Co0.8Fe0.2O3-δ用作SOEC阳极材料具有很好的应用前景.     

固态氧化物电解池中碳-分子电化学转化为可再生燃料

近年来,随着社会环保意识的迅速提高以及对可再生能源利用能力的大幅增强,以燃料电池和电解池为代表的电化学技术已经逐渐在能源的存储、转化和利用方面发挥着不可或缺的独特作用.其中,固态氧化物电解池经过多年的发展,在装置成本和工作效率上取得了长足的进步,在储能转化方面具有重要的潜力.与此同时,伴随着《巴黎协定》签订以来各国的“碳中和”路线图逐渐出台,利用相对廉价易得的可再生电能,将二氧化碳(CO₂)和甲烷(CH₄)等碳-(C1)分子电解转化为高附加值的可再生燃料(如水煤气、乙烯等),对于碳中和目标的实现具有重要的意义.因此,C1分子电化学转化的研究成为了当下重点关注的研究领域,许多重要的研究成果和技术进步在过去几年中不断涌现.固态氧化物电解池作为一种代表性的C1分子电解和转化平台,也日渐引起相关领域研究人员的关注和兴趣.与传统的C1分子催化转化方法相比,基于固态氧化物电解池的电解转化技术具有两个重要优点:高能量转换效率与体系抗中毒能力.这两个特性作为体系稳健性的基石,保障了C1分子转化为可再生燃料的反应过程的长期可持续性.本文首先简要回顾了固态氧化物电解池的前沿技术与发展,并从电解池系统分类、反应体系的特征和反应体系发展的前景与挑战这三个方面,简要介绍了近年来基于固态氧化物电解池体系的C1分子电化学转化的代表性工作.CO₂与CH₄作为廉价易得的C1分子的代表,其转化因其反应分子惰性及反应过程不可控性而广受研究者关注,本文重点关注了在固态氧化物电解池中CO₂,CO₂/H₂O和CH₄三个体系的电化学反应过程和近期研究进展,希望可为相关研究人员未来设计更合适的催化剂和构建更优的电解池结构提供有益的参考.本文还针对目前固态氧化物电解池体系在C1分子转化领域所面临的挑战,提出了未来的一些可能的研究方向,以期助力研究者在不远的将来实现C1分子电解生产可再生燃料的实用化.     

Electricity Storage With High Roundtrip Effciency in a Reversible Solid Oxide Cell Stack

We theoretically investigate the electricity storage/generation in a reversible solid oxide cell stack. The system heat is for the first time tentatively stored in a phase-change metal when the stack is operated to generate electricity in a fuel cell mode and then reused to store electricity in an electrolysis mode. The state of charge (H₂ frication in cathode) effectively enhances the open circuit voltages (OCVs) while the system gas pressure in electrodes also increases the OCVs. On the other hand, a higher system pressure facilitates the species diffusion in electrodes that therefore accordingly improve electrode polarizations. With the aid of recycled system heat, the roundtrip efficiency reaches as high as 92% for the repeated electricity storage and generation.     

Advance in highly efficient hydrogen production by high temperature steam electrolysis

High Temperature Steam Electrolysis (HTSE) through a solid oxide electrolytic cell (SOEC) has been receiving increasing research and development attention worldwide because of its high conversion efficiency (about 45%-59%) and its potential usage for large-scale production of hydrogen. The mechanism, composition, structure, and developing challenges of SOEC are summarized. Current situation, key materials, and core technologies of SOEC (solid oxide electrolytic cell) in HTSE are re- viewed, and the prospect of HTSE future application in advanced energy fields is proposed. In addition, the recent research achievements and study progress of HTSE in Tsinghua University are also intro- duced and presented.     

Electrochemical reduction of CO_2 in solid oxide electrolysis cells

The effort on electrochemical reduction of CO_2 to useful chemicals using the renewable energy to drive the process is growing fast recently. In this review, we introduce the recent progresses on the electrochemical reduction of CO_2 in solid oxide electrolysis cells(SOECs). At high temperature, only CO is produced with high current densities and Faradic efficiency while the reactor is complicated and a better sealing technique is urgently needed. The typical electrolytes such as zirconia-based oxides, ceria-based oxides and lanthanum gallates-based oxides, anodes and cathodes are introduced in this review, and the cathode materials, such as conventional metal–ceramics(cermets), mixed ionic and electronic conductors(MIECs) are discussed in detail. In the future, to gain more value-added products, the electrolyte, cathode and anode materials should be developed to allow SOECs to be operated at temperature range of 573–873 K. At those temperatures, SOECs may combine the advantages of the low temperature system and the high temperature system to produce various products with high current densities.     

Application of bipolar membrane technology: A novel process for control of sulfur dioxide from flue gases

We have demonstrated that the phenomenon of electrodialytic water splitting by bipolar membranes can be developed to a practical engineering unit process for the removal and recovery of SO₂ from stack gas. The SO₂ is first removed from the stack gas by means of an alkaline scrubbing solution. The spent solution is then regenerated in an electrodialysis cell containing only cation and bipolar membranes by the process known as two compartment electrodialytic water splitting. Concentrated SO₂ is liberated and recovered for further processing. p]Experimental results on our regeneration system show that an excellent current efficiency of 85% is obtained and that since the potential drop is only about 1.6 volts per cell unit, the system consumes less than half of the energy required for a conventional electrolysis acid base generation process. Tests have also shown that the bipolar membranes can satisfactorily be operated in the present system for long periods of time. This new process appears to be an attractive means of SO₂ abatement and could lead to the first commercial application of the new engineering principle of electrodialytie water splitting.     

Co-electrolysis of CO_2 and H_2O in high-temperature solid oxide electrolysis cells: Recent advance in cathodes

Co-electrolysis of CO_2 and H_2O using high-temperature solid oxide electrolysis cells(SOECs) into valuable chemicals has attracted great attentions recently due to the high conversion and energy efficiency,which provides opportunities of reducing CO_2 emission, mitigating global warming and storing intermittent renewable energies. A single SOEC typically consists of an ion conducting electrolyte, an anode and a cathode where the co-electrolysis reaction takes place. The high operating temperature and difficult activated carbon-oxygen double-bond of CO_2 put forward strict requirements for SOEC cathode. Great efforts are being devoted to develop suitable cathode materials with high catalytic activity and excellent long-term stability for CO_2/H_2O electro-reduction. The so far cathode material development is the key point of this review and alternative strategies of high-performance cathode material preparation is proposed. Understanding the mechanism of CO_2/H_2O electro-reduction is beneficial to highly active cathode design and optimization. Thus the possible reaction mechanism is also discussed. Especially, a method in combination with electrochemical impedance spectroscopy(EIS) measurement, distribution functions of relaxation times(DRT) calculation, complex nonlinear least square(CNLS) fitting and operando ambient pressure X-ray photoelectron spectroscopy(APXPS) characterization is introduced to correctly disclose the reaction mechanism of CO_2/H_2O co-electrolysis. Finally, different reaction modes of the CO_2/H_2O coelectrolysis in SOECs are summarized to offer new strategies to enhance the CO_2 conversion. Otherwise,developing SOECs operating at 300-600 °C can integrate the electrochemical reduction and the Fischer-Tropsch reaction to convert the CO_2/H_2O into more valuable chemicals, which will be a new research direction in the future.     

Fuel cell performance assessment for closed-loop renewable energy systems

Fuel cells and electrolysis are promising candidates for future energy production from renewable energy sources. Usually, polymer electrolyte fuel cell systems run on hydrogen and air, while the most of electrolysis systems vent out oxygen as unused by-product. Replacing air with pure oxygen, fuel cell electrochemical performance, durability and system efficiency can be significantly increased with a further overall system simplification and increased reliability. This work, which represents the initial step for pure H_2/O_2 polymer electrolyte fuel cell operation in closed-loop systems, focuses on performance validation of a single cell operating with pure H_2/O_2 under different relative humidity(RH) levels, reactants stoichiometry conditions and temperature. As a result of this study, the most convenient and appropriate operative conditions for a polymer electrolyte fuel cell stack integrated in a closed loop system were selected.     

Achieving High Efficiency and Eliminating Degradation in Solid Oxide Electrochemical Cells Using High Oxygen‐Capacity Perovskite

Recently, there have been efforts to use clean and renewable energy because of finite fossil fuels and environmental problems. Owing to the site‐specific and weather‐dependent characteristics of the renewable energy supply, solid oxide electrolysis cells (SOECs) have received considerable attention to store energy as hydrogen. Conventional SOECs use Ni‐YSZ (yttria‐stabilized zirconia) and LSM (strontium‐doped lanthanum manganites)‐YSZ as electrodes. These electrodes, however, suffer from redox‐instability and coarsening of the Ni electrode along with delamination of the LSM electrode during steam electrolysis. In this study, we successfully design and fabricate highly efficient SOECs using layered perovskites, PrBaMn₂O_5+δ (PBM) and PrBa_0.5Sr_0.5Co_1.5Fe_0.5O_5+δ (PBSCF50), as both electrodes for the first time. The SOEC with layered perovskites as both‐side electrodes shows outstanding performance, reversible cycling, and remarkable stability over 600 hours.     

Electrochemical hydrogen production from biomass

Thermodynamic data indicate that the oxidation of oxygenated organic species originating from biomass instead of water at the anode of an electrolysis cell should allow decreasing the cell voltage below 1.23 V. Biosourced alcohols, polyols, sugars, lignocellulosic compounds, and their derivatives are then electroreformed to produce clean hydrogen at the cathode and compounds at the anode of electrolysis cells. The reported studies highlight the main challenges to make electroreforming a future industrial process: higher reaction kinetics and hydrogen evolution rate; better selectivity of anode catalysts toward the formation of CO₂ or added-value compounds; and utilization of nonstrategical metals. An attractive solution to decrease hydrogen production costs and to make bankable other economic activities consists in directly valuing wastes from agriculture/forestry (lignocellulosic raw materials) and/or wastes from biofuel industries.     

氧分压对固体氧化物电解池性能的影响

High-temperature (700–900 ℃) steam electrolysis based on solid oxide electrolysis cells (SOECs) is valuable as an efficient and clean path for large-scale hydrogen production with nearly zero carbon emissions, compared with the traditional paths of steam methane reforming or coal gasification. The operation parameters, in particular the feeding gas composition and pressure, significantly affect the performance of the electrolysis cell. In this study, a computational fluid dynamics model of an SOEC is built to predict the electrochemical performance of the cell with different sweep gases on the oxygen electrode. Sweep gases with different oxygen partial pressures between 1.01 × 10³ and 1.0 × 10⁵ Pa are fed to the oxygen electrode of the cell, and the influence of the oxygen partial pressure on the chemical equilibrium and kinetic reactions of the SOECs is analyzed. It is shown that the rate of increase of the reversible potential is inversely proportional to the oxygen partial pressure. Regarding the overpotentials caused by the ohmic, activation, and concentration polarization, the results vary with the reversible potential. The Ohmic overpotential is constant under different operating conditions. The activation and concentration overpotentials at the hydrogen electrode are also steady over the entire oxygen partial pressure range. The oxygen partial pressure has the largest effect on the activation and concentration overpotentials on the oxygen electrode side, both of which decrease sharply with increasing oxygen partial pressure. Owing to the combined effects of the reversible potential and polarization overpotentials, the total electrolysis voltage is nonlinear. At low current density, the electrolysis cell shows better performance at low oxygen partial pressure, whereas the performance improves with increasing oxygen partial pressure at high current density. Thus, at low current density, the best sweep gas should be an oxygen-deficient gas such as nitrogen, CO₂, or steam. Steam is the most promising because it is easy to separate the steam from the by-product oxygen in the tail gas, provided that the oxygen electrode is humidity-tolerant. However, at high current density, it is best to use pure oxygen as the sweep gas to reduce the electric energy consumption in the steam electrolysis process. The effects of the oxygen partial pressure on the power density and coefficient of performance of the SOEC are also discussed. At low current density, the electrical power demand is constant, and the efficiency decreases with growing oxygen partial pressure, whereas at high current density, the electrical power demand drops, and the efficiency increases.     

Structural Evolution of Pt,Au and Cu Anodes by Electrolysis up to Contact Glow Discharge Electrolysis in Alkaline Electrolytes**

Applying a voltage to metal electrodes in contact with aqueous electrolytes results in the electrolysis of water at voltages above the decomposition voltage and plasma formation in the electrolyte at much higher voltages referred to as contact glow discharge electrolysis (CGDE). While several studies explore parameters that lead to changes in the I–U characteristics in this voltage range, little is known about the evolution of the structural properties of the electrodes. Here we study this aspect on materials essential to electrocatalysis, namely Pt, Au, and Cu. The stationary I–U characteristics are almost identical for all electrodes. Detailed structural characterization by optical microscopy, scanning electron microscopy, and electrochemical approaches reveal that Pt is stable during electrolysis and CGDE, while Au and Cu exhibit a voltage-dependent oxide formation. More importantly, oxides are reduced when the Au and Cu electrodes are kept in the electrolysis solution after electrolysis. We suspect that H₂O₂ (formed during electrolysis) is responsible for the oxide reduction. The reduced oxides (which are also accessible via electrochemical reduction) form a porous film, representing a possible new class of materials in energy storage and conversion studies.     

Innovative Electrochemical Strategies for Hydrogen Production: From Electricity Input to Electricity Output

Renewable H₂ production by water electrolysis has attracted much attention due to its numerous advantages. However, the energy consumption of conventional water electrolysis is high and mainly driven by the kinetically inert anodic oxygen evolution reaction. An alternative approach is the coupling of different half-cell reactions and the use of redox mediators. In this review, we, therefore, summarize the latest findings on innovative electrochemical strategies for H₂ production. First, we address redox mediators utilized in water splitting, including soluble and insoluble species, and the corresponding cell concepts. Second, we discuss alternative anodic reactions involving organic and inorganic chemical transformations. Then, electrochemical H₂ production at both the cathode and anode, or even H₂ production together with electricity generation, is presented. Finally, the remaining challenges and prospects for the future development of this research field are highlighted.     

高温固体氧化物电解制氢技术发展现状与展望

固体氧化物电解池是一种先进的能量转换装置,具有高效、简单、灵活、环境友好等特点,是目前国际能源领域的研究热点. 本文对高温固体氧化物电解制氢技术的基本原理、关键材料、系统组成、发展历程及国内外研究现状等进行了总结和分析,小结了该技术发展面临的主要挑战,简述了清华大学在高温固体氧化物电解领域近期的研究进展,并对其未来应用前景进行了展望.     

电化学合成纳米材料和小分子材料在电解制氢领域的应用

氢气是一种清洁、高效、可再生的新型能源,并且是未来碳中和能源供应中最具潜力的化石燃料替代品。因此,可持续氢能源制造具有极大的吸引力与迫切的需求,尤其是通过清洁、环保、零排放的电解水方法。然而,目前的电解水反应受到其缓慢的动力学以及低成本/能源效率的制约。在这些方面,电化学合成通过制造先进的电催化剂和提供更高效/增值的共电解替代品,为提高水电解的效率和效益提供了广阔的前景。它是一种环保、简单的通过电解或其他电化学操作,对从分子到纳米尺度的材料进行制造的方法。本文首先介绍了电化学合成的基本概念、设计方法以及常用方法。然后,总结了电化学合成技术在电解水领域的应用及进展。我们专注于电化学合成的纳米结构电催化剂以实现更高效的电解水制氢,以及小分子的电化学氧化以取代电解水制氢中的析氧共反应,实现更高效、 增值的共电解制氢。我们系统地讨论了电化学合成条件与产物的关系,以启发未来的探索。最后,本文讨论了电化学合成在先进电解水以及其他能量转换和储存应用方面的挑战和前景。     

An Electrolytic Zn–MnO2 Battery for High‐Voltage and Scalable Energy Storage

Zinc‐based electrochemistry is attracting significant attention for practical energy storage owing to its uniqueness in terms of low cost and high safety. However, the grid‐scale application is plagued by limited output voltage and inadequate energy density when compared with more conventional Li‐ion batteries. Herein, we propose a latent high‐voltage MnO₂ electrolysis process in a conventional Zn‐ion battery, and report a new electrolytic Zn–MnO₂ system, via enabled proton and electron dynamics, that maximizes the electrolysis process. Compared with other Zn‐based electrochemical devices, this new electrolytic Zn–MnO₂ battery has a record‐high output voltage of 1.95 V and an imposing gravimetric capacity of about 570 mAh g^?1, together with a record energy density of approximately 409 Wh kg^?1 when both anode and cathode active materials are taken into consideration. The cost was conservatively estimated at <US$ 10 per kWh. This result opens a new opportunity for the development of Zn‐based batteries, and should be of immediate benefit for low‐cost practical energy storage and grid‐scale applications.     

Tailoring Ion Ordering in Perovskite Oxide for High-Temperature Oxygen Evolution Reaction

Perovskites exhibit excellent high-temperature oxygen evolution reaction (OER) activities as the anodes of solid oxide electrolysis cells (SOECs). However, the relationship between ion ordering and OER performances is rarely investigated. Herein, a series of PrBaCo_2−xFe_xO_5+δ perovskites with tailored ion orderings are constructed. Physicochemical characterizations and density functional theory calculations confirm that the oxygen bulk migration and surface transport capacities as well as the OER activities are promoted by the A-site cation ordering, but weakened by the oxygen vacancy ordering. Hence, SOEC with the A-site-ordered and oxygen-vacancy-disordered PrBaCo₂O_5+δ anode exhibits the highest performance of 3.40 A cm⁻² at 800 °C and 2.0 V. This work sheds light on the critical role of ion orderings in the high-temperature OER performance and paves a new way for screening novel anode materials of SOECs.     

High performance solid oxide electrolysis cell with impregnated electrodes

Here we report a solid oxide electrolysis cell (SOEC) employing impregnated electrodes. The cell structure consisted of a porous 430 L metal support, a Ni-Ce_0.8Sm_0.2O_2 − δ (SDC) impregnated 430 L-zirconia stabilized zirconia (YSZ) hydrogen electrode, a scandia stabilized zirconia (SSZ) electrolyte and a Nd₂O₃-Nd₂NiO_4 + δ (Nd₂O₃-NNO) impregnated SSZ oxygen electrode. The cell is prepared by tape casting, co-firing and impregnation techniques. At an applied voltage of 1.3 V and 50% steam content, current density of 2.05 A cm^− 2 is obtained at 800 °C. The effect of the variation of H₂O/H₂ ratio (3/97 to 70/30) on electrolysis performance at 750 °C is evaluated and the long-term stability in electrolysis mode is also investigated.     

Power‐to‐Syngas: An Enabling Technology for the Transition of the Energy System?

Power‐to‐X concepts promise a reduction of greenhouse gas emissions simultaneously guaranteeing a safe energy supply even at high share of renewable power generation, thus becoming a cornerstone of a sustainable energy system. Power‐to‐syngas, that is, the electrochemical conversion of steam and carbon dioxide with the use of renewably generated electricity to syngas for the production of synfuels and high‐value chemicals, offers an efficient technology to couple different energy‐intense sectors, such as “traffic and transportation” and “chemical industry”. Syngas produced by co‐electrolysis can thus be regarded as a key‐enabling step for a transition of the energy system, which offers additionally features of CO₂‐valorization and closed carbon cycles. Here, we discuss advantages and current limitations of low‐ and high‐temperature co‐electrolysis. Advances in both fundamental understanding of the basic reaction schemes and stable high‐performance materials are essential to further promote co‐electrolysis.