Electrochemical Energy Conversion Devices Research Articles

Additive Manufacturing of Solid Oxide Fuel Cell (AM-SOFC) Stacks

The Solid oxide fuel cell (SOFC) is an electrochemical energy-conversion device which offers tremendous promise for delivering high electrical efficiency and significant environmental benefits in terms of fuel flexibility, as well as clean and efficient electric power generation. However, the state-of-the-art SOFC cell currently involves expensive and time-consuming multi-step manufacturing processes including tape casting, screen printing, shaping, lamination, sintering, etc. In addition, SOFC stacks are usually assembled with pre-fabricated cells, metal interconnects, and glass-ceramic sealing. These indispensable components add extra layers of complexity to the stack structure’s fabrication and maintenance, significantly increasing the size and weight of the final product. These intrinsic limitations on the current planar stack cannot be easily removed by traditional manufacturing processes. However, as additive manufacturing (AM) technologies start to mature and show increasing market penetration, it lends itself admirably to breaking the limits on high-power-density SOFC stack manufacturing. Storagenergy’s SOFC project is developing an all-ceramic AM-SOFC by a high-speed AM process of multiple materials. The developed technology allows the fabrication of robust and compact AM-SOFC stacks with unique features such as monolithic architecture with embedded novel micro flow channels and thinner elements (anode, cathode, electrolyte, and interconnect) by only three production steps (3D printing, sintering, and catalyst infiltration) without the need for subsequent assembly of individual layers and indispensable components. This simplification of the fabrication process is expected to reduce the cost of the SOFC and increase SOFC design flexibility and manufacturing reliability.

(Invited) Electrochemical Energy Storage and Conversion Devices Incorporating C2-Protected Polybenzimidazoliums and Polyimidazoliums

Alkaline anion exchange membranes which are capable of conducting hydroxide ions have broadly been applied in alkaline-based electrochemical energy storage and conversion technologies. Electrochemical systems relying on alkaline-based active components possess unique advantages over their acidic counterparts but at the same time are associated with significant challenges. There is a growing interest in C2-protected polybenzimidazoliums and polyimidazoliums as hydroxide ion conducting polymers for membranes and catalyst layers because of their high stability under caustic conditions, scalability in synthesis, and mechanical strength. This presentation will focus on recent progress in their preparation and on research trends incorporating these polymers into membranes, catalyst layers, and electrochemical energy storage and conversion devices. The challenges of integration that need to be overcome to meet critical requirements will be discussed, together with a summary and perspective for future directions.

(Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award Address) Anion Exchange and Bipolar Membranes for Electrochemical Energy Conversion and Storage

Ion-conducting membranes play a central role in electrochemical devices. The rise in anion exchange membrane fuel cell (AEMFC) research is attributed to the viability of using platinum-group-metal free electrocatalysts for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR).1 However, there are two major obstacles to apply anion exchange membranes (AEMs) as separators in alkaline electrochemical energy conversion devices. The first challenge is to develop the AEM with hydroxide ion conductivities above 100 mS/cm at 70 °C. The second challenge is to synthesize stable AEM (especially stable cationic head-groups) that exhibit high durability in strongly alkaline environments (e.g. in the presence of nucleophilic OH- ions). To solve the first problem, a triblock copolymer-based polymer backbone has been developed to synthesize AEMs with high ion conductivities by engineering a phase-separated morphology. To address the second problem, cycloaliphatic quaternary ammonium based AEM have been prepared that demonstrate excellent alkaline stability.Except for the performance of the separator, there are other factors including the design of electrocatalysts for HOR and ORR, and the structure of catalyst layer contributes to overall fuel cell performance. Herein, significant amount of effort has been made to better design the ionomer/electrocatalysts interface and to better understand the transport of the ionomer in confined regime. The use of a pH-gradient-enabled microscale bipolar interface (PMBI) to effectively separate the anolyte and catholyte of a direct borohydride/ hydrogen peroxide liquid fuel cell (DBFC) has been engineered and demonstrated, which enables record high DBFC performance. 2 The PMBI-type electrodes provide a new and fascinating design to engineer fuel-cell membrane electrode assemblies. Interdigitated electrode arrays (IDEs) have been developed as a platform for highly sensitive electrochemical measurements of polymer thin film with thickness of less than 100 nm.3 The IDEs coupled with electrochemical impedance spectroscopy (EIS) has been demonstrated as an effective platform to probe ion transport of polymer thin film, which provide direct translation to the design of the ionomer in fuel cell. References (1) Arges, C. G.; Zhang, L. Anion Exchange Membranes’ Evolution toward High Hydroxide Ion Conductivity and Alkaline Resiliency. ACS Applied Energy Materials 2018, 1 (7), 2991-3012, DOI: 10.1021/acsaem.8b00387.(2) Wang, Z.; Parrondo, J.; He, C.; Sankarasubramanian, S.; Ramani, V. Efficient pH-gradient-enabled microscale bipolar interfaces in direct borohydride fuel cells. Nature Energy 2019, DOI: 10.1038/s41560-019-0330-5.(3) Sharon, D.; Bennington, P.; Liu, C.; Kambe, Y.; Dong, B. X.; Burnett, V. F.; Dolejsi, M.; Grocke, G.; Patel, S. N.; Nealey, P. F. Interrogation of Electrochemical Properties of Polymer Electrolyte Thin Films with Interdigitated Electrodes. J Electrochem Soc 2018, 165 (16), H1028-H1039, DOI: 10.1149/2.0291816jes.

(Invited) Carbon Coatings for Components in Anion Exchange Membrane Electrochemical Energy Conversion

We at SMT are committed to using engineering and innovation to advance the world towards more sustainable business. We also understand the need to make the shift to new business models and new thinking in line with the UN’s Sustainable Development Goals and the Paris Climate Agreement. We are, moreover, fully aware that the intermittency of renewables poses significant challenges, but we believe that long-term energy storage by power-to-gas (e.g., the “Hydrogen Economy”) is an important pillar in overcoming those challenges. We imagine carbon as (almost) ideal (coating) material for low-temperature electrochemical energy conversion due to its sustainability, conductivity, low cost, and the fact that, unlike most metals and alloys, it does not form thick oxide layers increasing its contact resistance (CR). Therefore, we have evaluated a selection of materials (Ti, [carbon-coated] stainless steels, stainless nickel) towards its compatibility with alkaline environments in terms of contact resistance and dissolution properties. The outcome clearly demonstrates the superiority of the carbon-coated material at intermediate pH values (< 11) [1]. Finally, at SMT we have long outgrown the research stage and offer, today, graphite-like roll-to-roll coatings on metal substrates, like stainless steel, as convenient low-cost material for bipolar plates in all types of low-temperature electrochemical energy conversion devices.[1] Proch S, Stenström M, Eriksson L, Andersson J, Sjöblom G, Jansson A, et al. Coated stainless steel as bipolar plate material for anion exchange membrane fuel cells (AEMFCs). Int J Hydrogen Energy. 2020;45:1313-24.

Nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions

The oxygen reduction/evolution reactions (ORR/OER) are a key electrode process in the development of electrochemical energy conversion and storage devices, such as metal-air batteries and reversible fuel cells. The search for low-cost high-performance nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for ORR/OER alternatives to the widely-used noble metal-based catalysts is a research focus. This review aims to outline the opportunities and available options for these nanocarbon-based bifunctional electrocatalysts. Through discussion of some current scientific issues, we summarize the development and breakthroughs of these electrocatalysts. Then we provide our perspectives on these issues and suggestions for some areas in the further work. We hope that this review can improve the interest in nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for ORR/OER.

Two-step pyrolytic engineering to form porous nitrogen-rich carbons with a 3D network structure for Zn-air battery oxygen reduction electrocatalysis

It is of great urgency to design inexpensive and high-performance oxygen reduction reaction (ORR) electrocatalysts derived from biowastes as substitutes for Pt-based materials in electrochemical energy-conversion devices. Here we propose a strategy to synthesize three-dimensional (3D) porous nitrogen-doped network carbons to catalyze the ORR from two-step pyrolysis engineering of biowaste scale combined with the use of a ZnCl2 activator and a FeCl2 promotor. Electrochemical tests show that the synthesized network carbons have exhibited comparable ORR catalytic activity with a half-wave potential (~0.85 V vs. RHE) and outstanding cyclical stability in comparison to the Pt/C catalyst. Beyond that, a high electron transfer number (~3.8) and a low peroxide yield (<7.6%) can be obtained, indicating a four-electron reaction pathway. The maximum power density is ~68 mW cm−2, but continuous discharge curves (at a constant potential of ~1.30 V) for 12 h are not obviously declined in Zn-air battery tests using synthesized network carbons as the cathodic catalyst. The formation of 3D porous structures with high BET surface area can effectively expose the surface catalytic sites and promote mass transportation to boost the ORR activity. This work may open a new idea to prepare porous carbon-based catalysts for some important reactions in new energy devices.

Pushing the Limit of Ordered Mesoporous Materials via 2D Self‐Assembly for Energy Conversion and Storage

AbstractMaterial and energy efficiencies are two key parameters that benchmark the electrochemical energy conversion and storage devices (EECSDs). Maximizing both requires researchers to grasp the limits of the physiochemical properties of core electrode materials. Ordered mesoporous materials (OMMs) have been regarded as promising electrode materials; however, their intrinsic deficiencies (e.g., plugs, inaccessible pores, and surfaces) impose limits for wide applications. 2D ordered mesoporous materials (2DOMMs) featured with an extended lateral dimension and a nanometer thickness not only inherit the structure advantages of mesoporous materials, but also have a unique 2D ultrathin feature that can fully address the imperfections of conventional OMMs. Herein, recent achievements on the preparation of 2DOMMs by combining single micelle assembly strategy with 2D bottom‐up patterning techniques including the molecular/space confined, interfacial orientated, and surface limited assembly are focused. Special focus is devoted to the newly developed synthetic strategies and their fundamental mechanisms for accurate control of some key structural parameters. Recent advances of 2DOMMs in EECSDs are also highlighted, which suggest that 2DOMMs are excellent material platforms for developing new battery chemistry as well as targeting performance optimization and cost reduction. Finally, the challenges and prospects are proposed based on current development.

Spatially graded porous transport layers for gas evolving electrochemical energy conversion: High performance polymer electrolyte membrane electrolyzers

Decarbonizing society’s energy infrastructure is foundational for a sustainable future and can be realized by harnessing renewable energy for clean hydrogen and on-demand power with fuel cells. Here, we elucidate how graded porous transport layers (PTLs) are instrumental for high performance gas evolving electrochemical energy conversion devices, with an emphasis on polymer electrolyte membrane (PEM) electrolyzers. Spatially graded PTLs fabricated by vacuum plasma spraying are examined via in operando neutron imaging, electrochemical characterization, and pore network modelling. The results reveal the staggering benefits of positioning the lower porosity region adjacent to the catalyst layer and the higher porosity region adjacent to the flow field, which lead to current densities up to 4.5 A/cm2 with a 29 % reduction in cell potential, 38 % reduction in mass transport overpotential, and 50 % reduction in PTL gas saturation. The liquid water permeability of the PTL also enhances by an order of magnitude, with a drastic reduction in gas saturation adjacent to the catalyst layer. Custom graded PTLs have the potential to transform performance levels for a broad array of gas evolving electrochemical energy conversion devices.

Lignin-derived hierarchical porous carbon supported Pd nanoparticles as an efficient electrocatalyst for ethanol oxidation

Herein, lignin derived hierarchical porous carbon (LHPC) supported Pd nanoparticles (Pd/LHPC) were synthesized and developed as advanced electrocatalysts for ethanol oxidation. In the Pd/LHPC, the special hierarchical porous carbon with the interconnected micropores and mesopores uniformly distribute on the surface and walls of macropores can provide facile transport for electroactive species and more reaction available surface. The Pd/LHPC exhibits larger specific electrochemically active surface area, higher electrocatalytic activity and better stability toward the oxidation of ethanol than the black carbon (Vulcan XC-72) supported Pd (Pd/XC-72) and commercial Pd/C electrocatalysts. The strategy reported will open a new road to effectively use industrial waste to synthesize advanced carbon material for efficient electrocatalysts and other electrochemical energy-conversion devices.

Diagnosing Stagnant Gas Bubbles in a Polymer Electrolyte Membrane Water Electrolyser Using Acoustic Emission

The use of acoustic emission as a low-cost, non-destructive, and operando diagnostic tool has been demonstrated for a range of electrochemical energy conversion and storage devices, including polymer electrolyte membrane water electrolysers (PEMWEs) and fuel cells. In this work, an abrupt change in acoustic regime is observed during operation of a PEMWE as the current density is increased from 0.5 to 1.0 A cm^{-2}. This regime change is marked by a sudden drop in the number of acoustic hits, while hit duration, amplitude, and energy increase significantly. It is found that the change in acoustic regime coincides with a significant extension of the stagnant bubble region in the flow channels of the PEMWE, observed with high-speed optical imaging. These results demonstrate that acoustic emission can be used effectively as an operando diagnostic tool to monitor bubble formation (two-phase flow conditions) in PEMWEs, facilitating rapid testing or prototyping, and contributing to operational safety.

Recent Progress on Defect-rich Transition Metal Oxides and Their Energy-Related Applications.

The applications of many energy-related electrochemical energy conversion and storage devices are changing with each passing day. Oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) are the key steps in the commercial application of these energy conversion/storage equipment. Defect-rich transition metal oxides (TMOs), such as Co, Mn, Fe, Ni, etc., have always been one of the most promising electrocatalysts, which are cheap, easy to obtain, high in catalytic activity and stable during electrocatalysis. In this review, we first introduce the definition, classification, characteristics, and construction of defects. Then, the latest developments of defect-rich TMO electrocatalysts in electrocatalysis and energy conversion storage device is summarized. Furthermore, the relationship between defects and activity and the potential mechanism are also discussed. The defects in defect-rich TMOs can adjust the surface/interface electronic structure of the electrocatalyst, change the adsorption energy of the intermediate product, or increase the intrinsic catalytic activity of active sites, which are beneficial for enhanced catalytic performance. Finally, the current challenges and prospects of defect-rich TMO electrocatalysts are proposed. Therefore, the introduction of defects in TMO will be a potential strategy for the rational design of high-performance electrocatalysts in the future.

Ionomers for electrochemical energy conversion & storage technologies

Ionomers, which are used as polymer electrolyte membranes as well as catalyst binders in membrane electrode assemblies, are a key component of electrochemical energy conversion and storage technologies such as fuel cells, electrolyzers, and flow batteries. The use of ionomers in these clean energy technologies has a long history and there has been considerable progress in developing low-cost, high-performance ionomers in recent years. In this review article, we discuss some highlights from recent developments of ionomers with emphasis on chemically stable, mechanically durable, high-performance hydrocarbon ionomers and their state-of-the-art performance in electrochemical energy conversion devices. Future directions of ionomer research that are important to enhance our understanding and the remaining challenges related to device level applications are addressed.

Efficient bifunctional electrocatalysts for solid oxide cells based on the structural evolution of perovskites with abundant defects and exsolved CoFe nanoparticles

Solid oxide cells (SOCs) including solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices. However, the lack of highly active and stable fuel electrode materials impedes their practical applications. Herein, in-situ exsolved CoFe nanoparticles on perovskite matrixes with abundant defects are developed as bifunctional fuel electrocatalysts for SOCs from the Sr2FeMo1-xCoxO6−δ (x = 0, 0.15, 0.25, 0.45) precursor. Increasement of Co doping promotes CoFe alloy exsolution and the formation of more defects in the remaining perovskite matrix under reducing atmosphere at high temperatures. Consequently, with increasing Co dopant content, the electrocatalytic activity towards CO2 electrolysis and hydrogen (H2) fuel oxidation are both significantly enhanced for the reduced Sr2FeMo1-xCoxO6−δ. The reduced Sr2FeMo1-xCoxO6−δ with high Co doping content of x = 0.45 electrocatalysts also exhibits respectable coking resistance and excellent long-term stability. The high performance may be owing to the unique simultaneously in-situ formed nanoalloy-oxide heterostructure and electron-ion mixed conductive perovskite matrixes with abundant defects.

Defect Chemistry on Electrode Materials for Electrochemical Energy Storage and Conversion

AbstractEfficient and sustainable clean energy technology is an urgent need to solve energy crisis and alleviate environmental pollution. Reasonable design of electrode materials can effectively improve the performance of electrochemical energy storage and conversion devices. As an effective method to control the properties of electrode materials, defects have recently received extensive attention. Herein, in this review, we will systematically summarize the application of defect chemistry on electrode materials for electrochemical energy storage and conversion. Firstly, we mainly describe the research content of defect chemistry from three aspects, including defect construction, the dynamic evolution and regulation of defects. Based on those understanding, the applications of defect chemistry in fuel cells, metal‐ion batteries and carbon/nitrogen fixation are discussed, respectively. Finally, the existing challenges and future development prospects of defect chemistry are proposed. Overall, we hope this review could help readers to better understand and apply defect chemistry on electrode materials.

Recent progresses of micro-nanostructured transition metal compound-based electrocatalysts for energy conversion technologies

The rapid consumption of fossil fuels has caused increasingly climatic issues and energy crisis, which leads to the urgent demand for developing sustainable and clean energies. Electrocatalysts play a key role in the development of electrochemical energy conversion and storage devices. Especially, developing efficient and cost-effective catalysts is important for the large-scale application of these devices. Among various electrocatalyst candidates, earth abundant transition metal compound (TMC)-based electrocatalysts are being widely and rapidly studied owing to their high electrocatalytic performances. This paper reviews the recent and representative advances in efficient TMC-based electrocatalysts (i.e., oxides, sulfides, selenides, phosphides, carbides and nitrides) for energy electrocatalytic reactions, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Different compounds with different applications are summarized and the relative mechanisms are also discussed. The strategies for developing earth-abundant and low-cost TMC-based electrocatalysts are introduced. In the end, the current challenges and future perspectives in the development of TMC research are briefly discussed. This review also provides the latest advance and outlines the frontiers in TMC-based electrocatalysts, which should provide inspirations for the further development of low-cost and high-efficiency catalysts for sustainable clean energy technologies.

The Chalkboard: Picture Your Electrode: A Primer on Scanning Electrochemical Microscopy

Every electrochemical energy storage and conversion device requires electrodes to exchange charge with the electrolyte and move electrons through an external circuit. We are used to describing electrode performance in terms of single-valued, averaged measurements: a peak current, a charge transfer resistance, a capacitance, and a charge capacity. However, these characterizations escape the complexity of most practical materials. Electrodes are not idealized current collectors but rather heterogeneous surfaces on which individual features strongly influence device performance by dictating local charge transfer. Thus, it would be desirable to understand reactivity at such locality, whatever its length scale.

Mesoporous Materials for Electrochemical Energy Storage and Conversion

AbstractDeveloping high‐performance electrode materials is an urgent requirement for next‐generation energy conversion and storage systems. Due to the exceptional features, mesoporous materials have shown great potential to achieve high‐performance electrodes with high energy/power density, long lifetime, increased interfacial reaction activity, and enhanced kinetics. In this Essay, applications of mesoporous materials are reviewed in electrochemical energy conversion and storage devices. The synthesis, structure, and properties of mesoporous materials and their performance in rechargeable batteries, supercapacitors, fuel cells, and electrolyzers are discussed, providing practical details and enlightening comments on the construction of high‐performance mesoporous electrodes. Lastly, the research challenges and perspectives on mesoporous materials for the future development of energy conversion and storage devices are assessed.

A high-performance oxygen evolution electrocatalyst based on partially amorphous bimetallic cobalt iron boride nanosheet

The oxygen evolution reaction (OER) plays a crucial role in various electrochemical energy conversion devices, but it greatly suffers from sluggish kinetic. Therefore, developing economical and high-active electrocatalysts with superior durability and high efficiency for OER is still a huge challenge. Herein, a partially amorphous nanosheet-liked bimetallic cobalt iron boride is directly grown on the nickel foam (CoFeB-5-30 NS/NF) via a facile electroless plating method and adopted as a catalyst for OER. Benefiting from the rational designed nanosheet array which provides large surface areas and more open-pathways to obtain fast electron transportation and gas release, the resulted CoFeB-5-30 NS/NF catalyst exhibits excellent catalytic activity and superior electrochemical stability in alkaline medium. The obtained CoFeB-5-30 NS/NF exhibits an overpotential of 260 mV to reach the current density of 20 mA cm−2. Most importantly, the CoFeB-5-30 NS/NF possesses a small Tafel slope of 38 mV dec−1 and excellent stability with insignificant activity degradation after successive electrolytic measurement (for over 60 h) at 20, 50 and 100 mA cm−2 in 1.0 M KOH, respectively. This work provides a simple and rapid strategy to prepare bimetallic borides and broadens the way for the development of efficient OER catalysts.

Advances in Ceramic Thin Films Fabricated by Pulsed Laser Deposition for Intermediate-Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) as one of the clean electrochemical energy conversion devices have acquired increasing attention recently due to the high efficiency, low emission, and excellent fuel...

Construction of N-doped carbon nanotube encapsulated active nanoparticles in hierarchically porous carbonized wood frameworks to boost the oxygen evolution reaction

Architecture design and optimization are regarded as essential approaches for improving the catalytic performance toward oxygen evolution reaction. Inspired by the natural porosity and directional micro-channels of wood, a universal strategy that N-doped carbon nanotube encapsulated active nanoparticles rooted into carbonized wood framework is proposed. The as-prepared catalysts show ultrahigh activity and robust stability. Representatively, the FeNi-P encapsulated in N-doped carbon nanotubes grown on the carbonized wood frameworks (denoted as FeNi–P@NCNT/CW) exhibit an outstanding OER activity with an overpotential of 180 mV to reach 50 mA cm−2. As comparison, such catalysts integrated in nickel foam and carbon paper require higher overpotentials with 251 and 249 mV, respectively. Furthermore, a steady OER overpotential is maintained even tested for more than 200 h (4.2 % decay). The referred construction will open a new road to adopting renewable resources for preparing efficient electrocatalysts and other electrochemical energy-conversion devices.