Electrochemical cells and systems play a key role in a wide range of industry sectors. These devices are critical enabling technologies for renewable energy; energy management, conservation, and ...storage; pollution control/monitoring; and greenhouse gas reduction. A large number of electrochemical energy technologies have been developed in the past. These systems continue to be optimized in terms of cost, life time, and performance, leading to their continued expansion into existing and emerging market sectors. The more established technologies such as deep-cycle batteries and sensors are being joined by emerging technologies such as fuel cells, large format lithium-ion batteries, electrochemical reactors; ion transport membranes and supercapacitors. This growing demand (multi billion dollars) for electrochemical energy systems along with the increasing maturity of a number of technologies is having a significant effect on the global research and development effort which is increasing in both in size and depth. A number of new technologies, which will have substantial impact on the environment and the way we produce and utilize energy, are under development. This paper presents an overview of several emerging electrochemical energy technologies along with a discussion some of the key technical challenges.
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•Carbon/hydrocarbon assisted water electrolysis reviewed for clean hydrogen production.•Reviewed different electrochemical technologies using carbon fuels under development.•This ...technology has been progressed to different levels of maturity for different carbon sources.•This route of hydrogen production can lower the electric input and CO2 emissions from the carbon sources.
Hydrogen is mainly produced by natural gas reforming, which is a highly efficient process with low feedstock costs. However, the rising interest in clean technologies will increase the demand for hydrogen, meaning that other sources will need to be explored. Although coal is currently the major source of power generation, its demand appears to be declining due to the rise in electricity generated from renewable energy sources and the worldwide quest for low-emission power generation. Coal reserves worldwide are abundant, but new technologies would be needed to produce hydrogen from this feedstock. Coal gasification is one well-established technology for this purpose, but it is inefficient and produces high CO2 emissions. An alternative technology that has been investigated over the past few decades is carbon assisted water electrolysis. The basic process is water/steam electrolysis, with part of the energy required for the electrolysis provided by the chemical energy of coal, which reduces the overall electrical energy input. In addition to coal, the process can also use other carbon sources, such as biomass, alcohols or gaseous hydrocarbons. Several studies have investigated this electrochemical route of hydrogen production, employing different electrolytes in a wide temperature range (room temperature to 850 °C) under different process conditions. This paper presents a comprehensive review of carbon assisted water electrolysis, associated materials used and the challenges for the development of the technology at the commercial scale.
The major technologies being considered for the green hydrogen production are polymer electrolyte membrane (PEM) and solid oxide electrolysis (SOE). While PEM electrolysis technology is nearing ...commercialisation with units now being globally installed at tens of MW scale, SOE technology is still under development with units available only at 100s of kW scale and at much higher costs per kW. SOE due to its high operating temperatures (close to 800 °C) has the potential to reduce the electric energy input by up to 30% for the hydrogen production per tonne by using the low-cost thermal energy input available from the industrial or downstream synthesis processes. The SOE cathode, where steam electrolysis occurs, plays a crucial role in dictating the cell voltage losses and the stability of the cell operation that eventually has a large impact on the SOE efficiency and lifetime. The current state-of-the-art cathode materials based on Ni-YSZ pose many challenges. There is, therefore, a global effort to find alternative cathode materials suitable for steam electrolysis in SOE. This review critically reviews novel nanoengineered cathode materials and points to the fact that such materials synthesized using infiltration and exsolution techniques, in combination with advanced materials characterisation like high-temperature scanning probe microscopy and in situ Raman spectroscopy can be a right approach to find the suitable cathode materials for steam electrolysis in SOE. This, however, may need to be combined with a techno-economic analysis to provide the technical and economic viability of these materials for the SOE commercialisation.
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•High temperature steam electrolysis critically reviewed, focussing on cathode materials.•Conventional and alternative cathode materials briefed, and their challenges discussed.•Novel heterostructured materials and their drawbacks discussed in-depth.•Scope of further research around novel materials highlighted at the end.
•Cu-GDC cathodes tested for high temperature steam electrolysis.•Remarkably low polarisation resistance of 0.42 Ωcm2 at 1.60 V, 800 °C.•Optimum steam flow rate for maximum current density was ...governed by Cu wt%.
Rising concerns on CO2 emissions and depletion of fossil fuels have led to the quest for developing technologies that aim to produce hydrogen via renewables-powered zero-emission electrolytic pathways. Solid oxide electrolytic cell (SOEC) is such an emerging technology since it is expected to produce higher electric efficiency compared to other state-of-the-art electrolysers like proton exchange membrane (PEM) and alkaline electrolytic cell (AEL). However, SOEC technology is limited by a dearth of high-temperature redox stable electrocatalytically active cathode materials and is currently relying mainly on the materials used as fuel electrodes in solid oxide fuel cells (SOFC). This work investigates the electrochemical performance of three different cathodes comprising cermets of copper and gadolinia doped ceria (Cu-GDC) for steam electrolysis at 800 °C in tubular SOEC under varying steam flow conditions and applied voltages. Remarkably, a polarisation resistance as low as 0.42 Ωcm2 was obtained at 1.60 V with a corresponding Faradaic efficiency more than 95%. A comparison of the trends depicted by current density versus steam flow rate clearly indicated that at any operating temperature, optimum steam flow rate required for maximum current density was governed by the concentration of electrocatalytically active sites. Similarly, a comparison of the voltage-current characteristics of both the cells revealed that Cu content as low as 30 wt% can impart sufficient electronic conductivity as well as catalytic activity to achieve current densities only 15–20% lower than what is obtained with 70 wt% Cu. Finally, 90 min short-term testing of both the cells at 1.60 V under 23% H2/77% steam (v/v) indicated no signs of performance degradation.
With the rapidly declining cost of renewable energy, efficient ways are needed for its transportation between different regions. Hydrogen is becoming a major energy vector, with the key challenges of ...its storage and transportation commonly overcome by using ammonia for chemical storage of hydrogen energy. Ammonia, which is more energy dense than hydrogen and easier to transport, is a carbon-free alternative fuel that can be used in a variety of ways to generate power. Owing to their robustness and efficiency, solid-oxide fuel cells (SOFC) stand out as one of the most promising technologies that convert ammonia to electricity. Unlike other fuel cells, such as polymer electrolyte membranes, SOFCs do not require the fuel to be cleaned by energy-intensive external cracking and extensive cleaning; their high operating temperature provides the flexibility to crack the ammonia inside the anode or to use it directly. Here, we discuss experimental and numerical studies of ammonia SOFCs and critically review the status and opportunities for ammonia-fuelled SOFC technology. In the first section, we briefly outline the potential cathode and electrolyte materials for SOFCs. Only the anode component poses additional challenges with ammonia over the well-established hydrogen-fuelled SOFC technology, and this topic has been addressed in detail. Anode catalysts for ammonia decomposition, parameters affecting ammonia decomposition and anode catalyst degradation are also discussed. In the second section, we review the modelling studies for ammonia SOFCs. Finally, we run through the major commercial initiatives and demonstrations in green ammonia production and ammonia SOFCs.
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•The recent developments of ammonia fuelled SOFCs are presented.•Anode design parameters affecting NH3 decomposition in anode are discussed.•Cell performance degradation and anode poisoning while using NH3 fuel are presented.•Reviewed cell performance models including the NH3 decomposition kinetics in anode.•The technology status and recent demonstrations are outlined.
The major applications of PGMs are as catalysts in automotive industry, petroleum refining, environmental (gas remediation), industrial chemical production (e.g., ammonia production, fine chemicals), ...electronics, and medical fields. As the next generation energy technologies for hydrogen production, such as electrolysers and fuel cells for stationary and transport applications, become mature, the demand for PGMs is expected to further increase. Reserves and annual production of Ru, Rh, Pd, Ir, and Pt have been determined and reported. Based on currently available resources, there is around 200 years lifetime based on current demand for all PGMs, apart from Pd, which may be closer to 100 years. Annual primary production of 190 t/a for Pt and 217 t/a for Pd, in combination with recycling of 65.4 t/a for Pt and 97.2 t/a for Pd, satisfies current demand. By far, the largest demand for PGMs is for all forms of catalysis, with the largest demand in auto catalysis. In fact, the biggest driver of demand and price for Pt, Pd, and Rh, in particular, is auto emission regulation, which has driven auto-catalyst design. Recovery of PGMs through recycling is generally good, but some catalytic processes, particularly auto-catalysis, result in significant dissipation. In the US, about 70% of the recycling stream from the end-of-life vehicles is a significant source of global secondary PGMs recovered from spent auto-catalyst. The significant use of PGMs in the large global auto industry is likely to continue, but the long-term transition towards electric vehicles will alter demand profiles.
Hydrogen has been widely recognised as a key resource in transitioning towards a sustainable and decarbonised energy future. Of the available hydrogen production processes, solid oxide electrolysis ...is a promising way to produce green hydrogen via high temperature electrolysis. The high conversion efficiencies of solid oxide electrolysis systems combined with the ability to integrate this technology with downstream chemical syntheses plants make them very attractive compared to other electrolysis technologies. However, solid oxide electrolysis, to date is the least developed electrolysis technology from the point of view of large-scale commercialisation. In recent years, significant research on fabrication and testing of individual solid oxide electrolyser (SOE) cells has been reported which has led to a multi-fold improvement in cell performance. Improvements on a cell level, though do not directly translate to improvements on a stack and system-level scale. Scaling-up solid oxide electrolysers for higher hydrogen production rates is challenging. This review presents an overview of the experimental and modelling investigations of the stack and system-scale SOE technology. The current commercial status of the SOE systems is highlighted and further improvements needed for successful near and long-term commercialisation of the technology are discussed.
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•Solid oxide electrolyser systems are reviewed, with a focus on stacks and modules.•Experimental studies on solid oxide stack testing are discussed.•Numerical and system-level modelling-based studies are reviewed in depth.•Current status of commercial solid oxide electrolyser systems is highlighted.•Challenges and future outlook for the technology are discussed.
Environmental issues related to global warming are constantly pushing the fossil fuel-based energy sector toward an efficient and economically viable utilization of renewable energy. However, ...challenges related to renewable energy call for alternative routes of its conversion to fuels and chemicals by an emerging Power-to-X approach. Methane is one such high-valued fuel that can be produced through renewables-powered electrolytic routes. Such routes employ alkaline electrolyzers, proton exchange membrane electrolyzers, and solid oxide electrolyzers, commonly known as solid oxide electrolysis cells (SOECs). SOECs have the potential to utilize the waste heat generated from exothermic methanation reactions to reduce the expensive electrical energy input required for electrolysis. A further advantage of an SOEC lies in its capacity to co-electrolyze both steam and carbon dioxide as opposed to only water, and this inherent capability of an SOEC can be harnessed for in situ synthesis of methane within a single reactor. However, the concept of in situ methanation in SOECs is still at a nascent stage and requires significant advancements in SOEC materials, particularly in developing a cathode electrocatalyst that demonstrates activity toward both steam electrolysis and methanation reactions. Equally important is the appropriate reactor design along with optimization of cell operating conditions (temperature, pressure, and applied potential). This review elucidates those developments along with research and development opportunities in this space. Also presented here is an efficiency comparison of different routes of synthetic methane production using SOECs in various modes, that is, as a source of hydrogen, syngas, and hydrogen/carbon dioxide mixture, and for in situ methane synthesis.
A solid oxide electrolysis cell (SOEC) powered by a renewable source can convert CO2 into carbon monoxide, which is a valuable feedstock for a range of fuels and chemical processes. The cathode ...material of the SOEC is required to possess sufficient catalytic activity for CO2 reduction, and also sustain the thermal and electrical load cycling to which the SOEC would be subjected when coupled with an intermittent renewable source without an auxiliary electricity or thermal storage system. The operating conditions can become even more challenging if solar or waste heat from exothermic downstream industrial processes is to be embedded in the process. In this study, we evaluated a mixed ionic–electronic conducting composite (La0·80Sr0.20Sc0.05Mn0·95O3-δ–Gd0.20Ce0·80O1.95) material as an SOEC cathode. Along with initial electrochemical performance, we investigated the cell's response to accelerated ageing tests, including electrical load cycling and extreme thermal cycling. Factors leading to performance degradation were studied by electrochemical impedance spectroscopy and structural characterisation of the cathode before and after the test. Thermal cycling resulted in more pronounced effect on the cell degradation rate as compared to electrical load cycling.
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•La0·80Sr0.20Sc0.05Mn0·95O3-δ-Gd0.20Ce0·80O1.95 cathode is tested for CO2 electrolysis.•Solid oxide electrolyser (SOE) evaluated under variable electrical load and thermal conditions.•Thermal cycling caused more significant degradation as compared to load cycling.•Cathode cracking and current collector coarsening identified as major causes of cell degradation.•Integration of SOEs with thermal storage systems is suggested while coupling with renewable source.
CO
2
and steam/CO
2
electroreduction to CO and methane in solid oxide electrolytic cells (SOEC) has gained major attention in the past few years. This work evaluates, for the very first time, the ...performance of two different ZnO–Ag cathodes: one where ZnO nanopowder was mixed with Ag powder for preparing the cathode ink (ZnO
mix
–Ag cathode) and the other one where Ag cathode was infiltrated with a zinc nitrate solution (ZnO
inf
–Ag cathode). ZnO
mix
–Ag cathode had a better distribution of ZnO particles throughout the cathode, resulting in almost double CO generation while electrolysing both dry CO
2
and H
2
/CO
2
(4:1 v/v). A maximum overall CO
2
conversion of 48% (in H
2
/CO
2
) at 1.7 V and 700 °C clearly indicated that as low as 5 wt% zinc loading is capable of CO
2
electroreduction. It was further revealed that for ZnO
inf
–Ag cathode, most of CO generation took place through RWGS reaction, but for ZnO
mix
–Ag cathode, it was the synergistic effect of both RWGS reaction and CO
2
electrolysis. Although ZnO
inf
–Ag cathode produced trace amount of methane at higher voltages, with ZnO
mix
–Ag cathode, there was absolutely no methane. This seems to be due to strong electronic interaction between Zn and Ag that might have suppressed the catalytic activity of the cathode towards methanation.
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