Proton-conducting Solid Oxide Electrolysis Research Articles

Numerical Study on Biogas Refining System Combined with Proton-Conducting Solid Oxide Electrolyzer

Biogas refining system including methanation reactor and proton-conducting electrolysis cell has been proposed and investigated based on the simulation including mass and heat balance analysis. Based on the calculation results, carbon deposition was predicted to still occur at the cathode outlet even with the gas humidification when a conventional oxide-ion conducting electrolyte is applied to the electrolysis cell due to the enhanced carbon activity caused by oxide-ion transport from the cathode to the anode. In the case of the proton-conducting electrolyte applied solid oxide electrolysis cell, proton transport from the anode to the cathode was found to mainly promote reverse water-gas shift reaction and methanation reaction without any carbon deposition. Even though the calculation results should be verified by comparing with experimental results, the numerical study suggested that the biogas refining system combined with p-SOEC is a promising technology for generating carbon-neutral methane with a strongly suppressed risk of carbon deposition.

Three‐dimensional Modeling and Performance Optimization of Proton Conducting Solid Oxide Electrolysis Cell▴

AbstractIn this study, a three‐dimensional model is developed to study a novel proton conducting solid oxide electrolysis cell (H‐SOEC) with porous current collector to alleviate the H2O‐starvation problem in oxygen electrode. The comparison between conventional straight‐channel structure and the new porous structure is conducted in detail. It is found that the porous current collector can increase the flow uniformity and facilitate the diffusion of H2O, which in turn improves the average performance of the H‐SOEC. The electrolysis efficiency can be increased by 6.4% compared to straight‐channel structure. It is also found that the thermal neutral voltage is decreased when the porous current collector is adopted. Besides, the evaluation of syngas production for CO2‐supplied H‐SOEC is performed. Compared to H2 production, the efficiency of syngas production can be increased by up to 13.5%.

Energy storage and hydrogen production by proton conducting solid oxide electrolysis cells with a novel heterogeneous design

The proton-conducting solid oxide electrolysis cell is a promising technology for energy storage and hydrogen production. However, because of the aggressive humid condition in the air electrode side, the stability of electrolysis cells is still a concern. In addition, the energy efficiency needs further improvement before its practical application. In this work, considering both stability and energy efficiency, a novel heterogeneous design is proposed for proton-conducting solid oxide electrolysis cells. In this heterogeneous design, the merits of proton-conducting materials can be taken advantage of and the drawbacks of proton-conducting materials can be circumvented synchronously, resulting in better stability and higher efficiency of electrolysis cells. The feasibility and advantages of the heterogeneous design are demonstrated in electrolysis cells with yttrium and zirconium co-doped barium cerate-nickel as the fuel electrode material and yttrium-doped barium zirconate as the electrolyte material by experiment and modeling. The experimental results demonstrate that compared with the conventional homogeneous design, this novel design can efficiently improve the proton conductivity of the yttrium-doped barium zirconate electrolyte (from 0.88 × 10−3 S cm−1 to 2.13 × 10−3 S cm−1 at 873 K) and slightly improve the ionic transport number of the electrolyte (from 0.941 to 0.964 at 873 K), resulting in better electrochemical performance. The electrolysis cells with this design also show good stability. Moreover, the simulation results show that the faradaic efficiency and energy efficiency of electrolysis cells are improved by applying this novel design. These impressive results demonstrate that heterogeneous design is a rational design for high-performance and efficient proton-conducting solid oxide electrolysis cell.

Performance Modeling of Hydrogen-Production Electrolysis Cells for Scaling up Electrochemical Materials

This presentation will introduce modeling methods of an electrochemical cell and correspondent computational tools that enable the implementation of materials into a component design for assessing their performance, lifetime and reliability through high-fidelity modeling methods. The component modeling tools use ANSYS software as a solution framework, by adding fundamental thermochemical, electrochemical, and thermomechanical models, for simulations from basic material properties to a full-product design. The thermochemical and electrochemical modeling tools were developed from the fundamental transport and chemical processes from basic material performance data and correlations to reduce prediction uncertainties. By incorporating the specific mathematical descriptions for hydrogen-production processes, the modeling methods can be adapted to various electrolysis cell types as a general approach for electrolysis device design or performance optimization, because a common solver platform is used and expands the functionality of the computational fluid dynamics (CFD) software, ANSYS/Fluent with an add-on electrochemical module through Fluent’s User Defined Function (UDF). Particularly, we have developed models for high-temperature electrolysis (HTE) using proton-conducting solid oxide electrolysis cell (H-SOEC), low-temperature electrolysis (LTE) of proton-exchange-membrane electrolysis cell (PEMEC), and carbon-dioxide reduction (CO2R) cells.These multi-scale electrochemical modeling tools have been used for component performance simulations and are for studying material implementation at the cell and stack level. Appropriate mathematical descriptions of the electrochemical and thermochemical processes were developed for a given system based on the underlying material performance taken from either experimental data or theoretical modeling results. The modeling practices were previously successfully applied to fuel cell design and transformed for electrolysis cell design. The integral modeling tool provides insights into new materials or components that can be or are being implemented into electrochemical cell and stacks. Furthermore, the computational tools can support the electrolyzer design, performance, degradation and life cycle predictions, and may accelerate the material implementation into a product with proper design and optimum performance conditions.The presentation will show that the computational modeling links experimental materials research with a component or product using high-fidelity thermochemical and electrochemical models. The focus of this presentation will be on the modeling method and results for the H-SOEC electrolysis cells. The approach will facilitate material R&D in general and improve the computational tools to support industry for predicting product and life cycle performance. Validation of component performance and system integration results against prototype designs can allow iterative improvements to the model and to various types, processes, and scales of systems.

A Proton Conducting Solid Oxide Electrolysis Cell with Tri-Doping Electrolyte and Three-Phase Conducting Steam Electrode for Sustainable Hydrogen Production

Proton conducting solid oxide electrolysis cell (P-SOEC) is an emerging technology that enables sustainable hydrogen production at reduced operating temperatures (400~600 ○C). Economically competitive P-SOEC systems have distinct advantages over conventional oxygen-ion conducting counterpart (O-SOEC), but further technology development and widespread market acceptance will require continuous innovation of materials in order to improve cell performance, enhance system lifetime and reduce cost. In this work, a new type of tri-doping barium-zirconium-cerate electrolyte and a triple phase conducting steam electrode are explored as material candidates. The material synthesis, pellet sintering, and electrical conductivity are carried out to evaluate the feasibility as an electrolyte. For the triple phase conducting electrode, the conduction behavior and catalytic activity towards water splitting reaction are studied. In addition, these two materials are incorporated into P-SOEC button cells and the electrochemical performance is evaluated under different operating conditions (temperature, humidity, feed gas composition, etc). The long-term durability in high steam pressure is also carried out to examine the stability of the material system. Such an early-stage R&D showed feasibility of hydrogen production systems for field operations and the ability to cost effectively produce hydrogen at the scale needed to support military operations.

Mathematical Modeling of a Proton-Conducting Solid Oxide Electrolyzer Cell Using Computational Fluid Dynamics Simulation

The proton-conducting solid oxide electrolyzer cell (H-SOEC) is a novel electrolysis technology, which operates in the intermediate temperature range (500-700°C), as opposed to the high temperature (800-1000°C) operating range of oxygen ion conducting solid oxide electrolysis cells (O-SOECs), or the low temperature (70-80°C) operating range of proton-exchange membrane (PEM) electrolyzers [1]. Proton-conducting electrolyte has high ionic conductivity in this intermediate temperature range, which is not exhibited in O-SOECs; this means that there are fewer material challenges for the development of these devices because they do not need to withstand temperatures up to 1000°C [1,2]. Additionally, this temperature ranges yields the benefits of improved thermodynamics at increased temperature, meaning they require less electrical energy input as compared to PEM electrolyzers [1]. H-SOECs are a promising technology because they retain the thermodynamic benefits of operation at high temperature, without the material complications seen in O-SOECs. The purpose of this work is to model the 2D current density distribution of an H-SOEC at a applied electrolysis voltage. The model considers overpotential losses that occur due to kinetics of the electrochemical reaction, resistance in the cell components, and mass transport. The mathematical model uses electrochemical parameters fit with experimental data from [3] and is incorporated into the solving routine of computational fluid dynamics (CFD) software, Fluent. Figure 1 shows an example of the current density distribution in a planar H-SOEC cell that was obtained from the model simulation. Such parametric distribution is difficult to be measured, and the outcomes of this work would help the experimental development of this novel electrolyzer technology through optimization of operating conditions like temperature and gas feed compositions. The modeling approach also helps understand the thermal-flow management needs of this device as it is scaled up to the stack level. It will also provide a baseline understanding for more complex models that consider the internal transport phenomena in 3D, as only limited modeling papers on H-SOEC are available now.

(Invited) High Performing and Stable Proton-Conducting Solid Oxide Electrolysis Cells with Triple Conducting Anodes

Proton-conductors BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and La2Ce2O7 (LDC) are combined to create an interface active and steam-tolerant electrolyte for high-performance proton-conducting solid oxide electrolysis cells. LDC shows good chemical compatibility with BZCYYb. The readily fabricated LDC/BZCYYb bilayer electrolyte can be densified at a temperature as low as 1300oC vs. ~1600oC for the benchmark vapor-stable BaZr0.8Y0.2O3-δ electrolyte. With Pr2NiO4+δ as the anode and Ni as the cathode catalyst, this bilayer electrolyte cell yields a current density of 975 mA/cm2 and 300 mA/cm2 under a 1.3 V applied potential at 700oC and 600oC, respectively. This performance is among the best of all H-SOECs equipped with a chemically stable electrolyte so far. BZCYYb layer in the bilayer electrolyte promotes the hydrogen evaluation reaction at the cathode side, resulting in a 108% improvement over the cell without this layer. The LDC layer, on the other hand, effectively protects this functional BZCYYb layer from high concentration of vapor in a practical SOEC operation condition. The cell without LDC layer shows degradation in terms of increase in the electrolyzing potential from 1.07 V to 1.29 V during a 400 mA/cm2 operation at 700oC. In contrast, the bilayer electrolyte cell maintains the same electrolyzing potential of 1.13 V under the same conduction for a 102 h operation. These findings demonstrate that this synergic bilayer electrolyte design could be a vital strategy to overcome the dilemma between performance and stability faced by the current benchmark Zr- or Ce-rich Ba(CeZr)O3-δ electrolytes, achieving good performance and stability at the same time.

(Invited) Performance Modeling of Hydrogen-Production Electrolysis Cells for Scaling up Electrochemical Materials

This presentation will introduce modeling methods of an electrochemical cell and correspondent computational tools that enable the implementation of materials into a component design for assessing their performance, lifetime and reliability through high-fidelity modeling methods. The component modeling tools use ANSYS software as a solution framework, by adding fundamental thermochemical, electrochemical, and thermomechanical models, for simulations from basic material properties to a full-product design. The thermochemical and electrochemical modeling tools are developed from the fundamental transport and chemical processes from basic material performance data and correlations to reduce prediction uncertainties. By incorporating the specific mathematical descriptions of hydrogen-production processes, the modeling methods can be adapted to various electrolysis cell types as a general tool for electrolyzer design or performance optimization, because a common solver platform was used and expands the functionalities of the computational fluid dynamics (CFD) software, ANSYS/Fluent with an add-on electrochemical module based on Fluent User Defined Function (UDF). In particularly, we have developed models for high-temperature electrolysis (HTE) using proton-conducting solid oxide electrolysis cell (H-SOEC), low-temperature electrolysis (LTE) of proton-exchange-membrane electrolysis cell (PEMEC), and carbon-dioxide reduction (CO2R) cells. The multi-scale electrochemical modeling tools have been used for component performance simulations and are for material scale-up and implementation in cell and stack level. Appropriate mathematical descriptions of the electrochemical and thermochemical processes need to be developed for a given system based on the underlying material performance from either experimental data or theoretical modeling results. The modeling practices were previously successfully applied for fuel cell design and transformed to electrolysis cells. The integral modeling tool provides insights for the new materials or components to be implemented into electrochemical cell and stacks. The computational tools can support the electrolyzer design, performance, degradation and life cycle predictions, and can accelerate the material implementation into a product with proper design and optimum performance. The presentation will show that the computational modeling links experimental materials research integrated into a component or product using high-fidelity thermochemical and electrochemical models. The focus of this presentation will be on modeling method and results for H-SOEC electrolysis cells. The approach will facilitate material R&D in general and improve the computational tools to support industry for predicting product and life cycle performance. Validation of component performance and system integration results against prototype designs can allow iterative model improvement and enhance for various types, processes, and scales of systems.

Progress Report on Proton Conducting Solid Oxide Electrolysis Cells

AbstractThe proton‐conducting solid oxide electrolysis cell (H‐SOEC) is a promising device that converts electrical energy to chemical energy. H‐SOECs have been actively studied in the past few years, due to their advantages over oxygen‐ion‐conducting solid oxide electrolysis cells (O‐SOECs), such as lower operation temperature, relatively lower activation energy, and easier gas separation. A critical overview of recent progress in H‐SOECs is presented, focusing particularly on the period from 2014 to 2018. This review focuses on three aspects of H‐SOECs, namely, the materials, modeling, and current leakage in proton conducting oxide electrolytes. Specifically, the current leakage in proton conducting oxides, which is often neglected, leads to two problems in the studies of H‐SOECs. One is the distortion of the electrochemical impedance spectra and the other is low faradaic efficiency of electrolysis. Based on the comprehensive and critical discussion in these three sections, challenges in the development of H‐SOECs are highlighted and prospective research in H‐SOECs is outlined.

Synergistic Coupling of Proton Conductors BaZr0.1Ce0.7Y0.1Yb0.1O3-δ and La2Ce2O7 to Create Chemical Stable, Interface Active Electrolyte for Steam Electrolysis Cells.

For the first time, proton conductors BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and La2Ce2O7 (LCO) are combined to create an interface active and steam-tolerant electrolyte for high-performance proton-conducting solid oxide electrolysis cells. LCO shows good chemical compatibility with BZCYYb. The readily fabricated LCO/BZCYYb bilayer electrolyte can be densified at a temperature of as low as 1300 °C versus ∼1600 °C for the benchmark steam-stable BaZr0.8Y0.2O3-δ electrolyte. With Pr2NiO4+δ as the anode and Ni as the cathode catalyst, this bilayer electrolyte cell yields a current density of 975 and 300 mA/cm2 under a 1.3 V applied potential at 700 and 600 °C, respectively. This performance is among the best of all H-SOECs equipped with a chemically stable electrolyte so far. A BZCYYb layer in the bilayer electrolyte promotes the hydrogen evolution reaction at the cathode side, resulting in a 108% improvement over the cellwithoutthis layer. The LCO layer, on the other hand, effectively protects this functional BZCYYb layer from the high concentration of steam in a practical SOEC operation condition. The cell without the LCO layer shows degradation in terms of an increased electrolyzing potential from 1.07 to 1.29 V during a constant 400 mA/cm2 operation at 700 °C. In contrast, the bilayer electrolyte cell maintains the same electrolyzing potential of 1.13 V under the same conduction for a 102 h operation. These findings demonstrate that this synergic bilayer electrolyte design is a vital strategy to overcome the dilemma between performance and stability faced by the current benchmark Zr- or Ce-rich Ba(CeZr)O3-δ electrolysis cells to achieve excellent performance and stability at the same time.

Concept, design, and energy analysis of an integrated power-to-methanol process utilizing a tubular proton-conducting solid oxide electrolysis cell

An alternative power-to-methanol process based on an integration of a tubular proton-conducting solid oxide electrolysis cell into a methanol synthesis unit is explained, energetically evaluated and technically presented. Being currently developed in the joint research project DELTA, the novel process has the potential for a significant increase in system efficiency, if the heat from the exothermic synthesis reaction can be utilized and/or kinetic advantages can be achieved. For the experimental proof of the concept and a comprehensive characterization of the process, a test platform is currently under construction. The design of the flexible test facility with the complex technical integration of both processes (electrolysis and synthesis) is described briefly. The chemical reactor, where electrolysis and synthesis are taking place, allows for an operation at temperatures (for electrolysis) up to 700 °C, pressures of 10 MPa and a current (across the electrolysis cell) of up to 100 A. Moreover, a precise pressure balancing system between both gas volumes, an axial temperature measurement and the possibility of regulating both processes inside the pressure vessel are pivotal properties of the test facility.

3D Self-Architectured Steam Electrode Enabled Efficient and Durable Hydrogen Production in a Proton-Conducting Solid Oxide Electrolysis Cell at Temperatures Lower Than 600 °C.

Hydrogen production via water electrolysis using solid oxide electrolysis cells (SOECs) has attracted considerable attention because of its favorable thermodynamics and kinetics. It is considered as the most efficient and low‐cost option for hydrogen production from renewable energies. By using proton‐conducting electrolyte (H‐SOECs), the operating temperature can be reduced from beyond 800 to 600 °C or even lower due to its higher conductivity and lower activation energy. Technical barriers associated with the conventional oxygen‐ion conducting SOECs (O‐SOECs), that is, hydrogen separation and electrode instability that is primarily due to the Ni oxidation at high steam concentration and delamination associated with oxygen evolution, can be remarkably mitigated. Here, a self‐architectured ultraporous (SAUP) 3D steam electrode is developed for efficient H‐SOECs below 600 °C. At 600 °C, the electrolysis current density reaches 2.02 A cm−2 at 1.6 V. Instead of fast degradation in most O‐SOECs, performance enhancement is observed during electrolysis at an applied voltage of 1.6 V at 500 °C for over 75 h, attributed to the “bridging” effect originating from reorganization of the steam electrode. The H‐SOEC with SAUP steam electrode demonstrates excellent performance, promising a new prospective for next‐generation steam electrolysis at reduced temperatures.

A New Triple-Conducting Material for Efficient Hydrogen Production in Proton Conducting Solid Oxide Electrolysis Cells

Steam electrolysis through solid oxide electrolysis cells (SOECs), are promising alternatives to steam reforming reaction for hydrogen generation in specific applications owing to its very high efficiency and clean products. However, the state-of-art SOEC relied on oxygen ion conductors (O-SOECs) that were required to be operated at high temperatures (>850oC). Proton conducting SOECs (P-SOECs) are emerging technologies that used proton conductor as the electrolyte and can be run at reduced temperatures, overcoming those O-SOECs’ problems such as fast degradation, and hydrogen separation, etc. The challenges of P-SOEC is poor performance with sluggish electrode kinetics at reduced temperatures as well as unproven stability. In this work, we report our findings in design, fabrication, and characterization of an extremely highly efficient P-SOEC with a novel triple-conducting steam electrode below 600oC in INL. The performance and durability of the P-SOECs exhibited significant improvement in comparison to those existing O-SOECs and P-SOECs.

Analysis of the Anode Reaction of Solid Oxide Electrolyzer Cells with BaZr0.4Ce0.4Y0.2O3-δ Electrolytes and Sm0.5Sr0.5CoO3-δ Anodes

Anodic reaction pathways in proton-conducting solid oxide electrolyzer cells (H+−SOECs) were investigated using electrochemical impedance spectroscopy with a cell structure of Sm0.5Sr0.5CoO3 (anode) | BaZr0.4Ce0.4Y0.2O3-δ | Pt (cathode). Densely sintered BaZr0.4Ce0.4Y0.2O3-δ ceramics (>97% relative density) were fabricated by a reactive sintering process with a 2 mol% Zn(NO3)2 additive and were applied as the electrolyte. The impedance spectra were measured while the oxygen (pO2) and water partial pressures (pH2O) in the anode side were systematically varied, which revealed that the SOECs have two polarization resistances at the anode side, one proportional to pO2−1/4 and pH2O0 and another insensitive to pO2 and pH2O. A comparison between the experimental results and elementary step modeling revealed that the actual anode reactions could be described by the reverse mode H+-SOFC cathode reactions, and, thus, the elementary steps dominating the anodic polarization resistance were assigned.

Development of High Performance Intermediate Temperature Proton-Conducting Solid Oxide Electrolysis Cells

Steam electrolysis by solid oxide fuel cell technology, known as SOEC, is considered the most efficient and cost effective option for hydrogen production from renewable sources. By using proton-conducting electrolyte, the SOEC operating temperature can be reduced from over 800oC to below 600oC. Technical barriers associated with the conventional oxygen-ion conducting SOECs, such as hydrogen separation from water, oxidation of steam electrode, and instability of oxygen electrode, can be largely mitigated. In this report, an intermediate temperature (400-600°C) electrolysis technology was developed where a novel proton-conductor and a triple-conducting oxide were used as the electrolyte and anode, respectively. The electrolysis cell demonstrated excellent performance and durability at intermediate temperatures, promising a new prospective for next-generation steam electrolysis.

Development of High Performance Intermediate Temperature Proton-Conducting Solid Oxide Electrolysis Cells

Steam electrolysis by solid oxide fuel cell technology, known as SOEC, is considered one of the most efficient and cost effective options for hydrogen production from renewable sources. By using proton-conducting electrolyte, the SOEC operating temperature can be reduced from over 800oC to below 600oC due to higher conductivity and lower activation energy. Technical barriers associated with the conventional oxygen-ion conducting SOECs, such as hydrogen separation from water, oxidation of steam electrode, and instability of oxygen electrode, can be largely mitigated. In this report, an intermediate temperature (500-600oC) electrolysis technology was developed where a novel proton-conductor and a triple-conducting oxide were used as the electrolyte and oxygen electrode, respectively. The electrolysis cell demonstrated excellent performance at intermediate temperatures, promising a new prospective for next-generation steam electrolysis.

Synthesis and Evaluation of Ni Catalysts Supported on BaCe0.5Zr0.3−xY0.2NixO3−δ with Fused-Aggregate Network Structure for the Hydrogen Electrode of Solid Oxide Electrolysis Cell

Nickel nanoparticles loaded on the electron–proton mixed conductor BaCe0.5Zr0.3−xY0.2NixO3−δ (Ni/BCZYN, x = 0 and 0.03) were synthesized for use in the hydrogen electrode of a proton-conducting solid oxide electrolysis cell (SOEC). The Ni nanoparticles, synthesized by an impregnation method, were from 45.8 nm to 84.1 nm in diameter, and were highly dispersed on the BCZYN. The BCZYN nanoparticles, fabricated by the flame oxide synthesis method, constructed a unique microstructure, the so-called “fused-aggregate network structure”. The BCZYN nanoparticles have capability of constructing a scaffold for the hydrogen electrode with both electronically conducting pathways and gas diffusion pathways. The catalytic activity on Ni/BCZYN (x = 0 and 0.03) catalyst layers (CLs) improved with the circumference length of the Ni nanoparticles. Moreover, the catalytic activity on the Ni/BCZYN (x = 0.03) CL was higher than that of the Ni/BCZYN (x = 0) CL. BCZYN (x = 0.03) possesses higher electronic conductivity than BCZYN (x = 0) due to the Ni doping, resulting in an enlarged effective reaction zone (ERZ). We conclude that the proton reduction reaction in the ERZ was the rate-determining step on the hydrogen electrode, and the reaction was enhanced by improving the electronic conductivity of the electron–proton mixed conductor BCZYN.

A novel design of solid oxide electrolyser integrated with magnesium hydride bed for hydrogen generation and storage – A dynamic simulation study

This paper proposes a novel solid oxide steam electrolyser with in-situ hydrogen storage by integrating a magnesium hydride (MH) section with proton-conducting solid oxide electrolysis cell (SOEC) section. Dynamic simulation results show that it takes 1950 s to fully charge the MH section with a 56% H2 storage efficiency without any flow recirculation, when the electrolyser is operated at 1.4V and 4atm, yielding a current density of 4956.40 A/m2. The evolution of temperature, H2 partial pressure and reaction of Mg powder through the charging process are analysed. It is found that the exothermic H2 absorption process of MH section can enhance the performance of the electrolysis process of SOEC section. The effects of operating parameters including operating pressure, electrolysis voltage, and cooling air temperature on the performance of the novel design are investigated by sensitivity studies. Results show that it is beneficial to operate the electrolyser at elevated pressure for shorter absorption time and higher H2 storage efficiency. Increasing the operating voltage can shorten the absorption time, but lower H2 storage efficiency. An optimal cooling air temperature is found at 521K when the electrolyser is operated at 1.4V and 4atm.

Computational design of cobalt-free mixed proton–electron conductors for solid oxide electrochemical cells

Proton-conducting solid-oxide electrolyzer and fuel cells (PC-SOECs/FCs) with new oxide-based electrodes represent viable, green technologies for H2 production and conversion.

Intermediate-temperature solid oxide electrolysis cells with thin proton-conducting electrolyte and a robust air electrode

A proton-conducting solid oxide electrolysis cell (H-SOEC) is a promising device that efficiently converts electrical energy to chemical energy.