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.
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.
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.
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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•Ethanol assisted water electrolysis reduces electric energy input by more than 50%.•Partial oxidation of ethanol leads to formation of undesired chemicals.•Degradation occurs due to ...formation of by-products and poisoning of catalyst.•Better catalyst has the potential to increase ethanol to H2 conversion efficiency.•A plausible ethanol electro-oxidation mechanism has been proposed
The global interest in hydrogen/fuel cell systems for distributed power generation and transport applications is rapidly increasing. Many automotive companies are now bringing their pre-commercial fuel cell vehicles in the market, which will need extensive hydrogen generation, distribution and storage infrastructure for fueling of these vehicles. Electrolytic water splitting coupled to renewable sources offers clean on-site hydrogen generation option. However, the process is energy intensive requiring electric energy >4.2kWh for the electrolysis stack and >6kWh for the complete system per m3 of hydrogen produced. This paper investigates using ethanol as a renewable fuel to assist with water electrolysis process to substantially reduce the energy input. A zero-gap cell consisting of polymer electrolyte membrane electrolytic cells with Pt/C and PtSn/C as anode catalysts were employed. Current densities up to 200mAcm−2 at 70°C were achieved at less than 0.75V corresponding to an energy consumption of about 1.62kWhm−3 compared with >4.2kWhm−3 required for conventional water electrolysis. Thus, this approach for hydrogen generation has the potential to substantially reduce the electric energy input to less than 40% with the remaining energy provided by ethanol. However, due to performance degradation over time, the energy consumption increased and partial oxidation of ethanol led to lower conversion efficiency. A plausible ethanol electro-oxidation mechanism has been proposed based on the Faradaic conversion of ethanol and mass balance of the by-products identified and quantified using 1H nuclear magnetic resonance spectroscopy and gas chromatography.
A carbon fuel cell (CFC) is an emerging technology for conversion of solid carbonaceous material into electricity at high theoretical efficiencies (100 %). As carbonaceous material like coal will ...remain an important energy source for the next few decades, the development of technology that can use it more efficiently is critical to reduce emissions. For practical operation of a CFC, a continual supply or consecutive refuelling of solid carbon fuel is required. Here, we investigated the electrochemical performance and durability of a CFC using a scandia-zirconia tubular electrolyte with Ce
0.9
Gd
0.1
O
2
–Ag electrodes with activated charcoal fuel. We demonstrated that CFCs can be operated in a batch-type process with refuelling and utilisation of fuel. Peak power densities up to 280 mW cm
−2
were obtained without major materials degradation. We expect that advances to engineering of fuel delivery will improve the long-term stability and performance of the cells.
There is an increasing interest in the exploration of non‐Nickel cathode materials for steam electrolysis in solid oxide electrolysis cells (SOEC) for green hydrogen production with high Faradaic ...efficiencies. Ferrite‐based ceramic materials have drawn a lot of attention in this regard due to their appreciable mixed ionic electronic conductivity. This work aims to explore a ferrite‐based mixed ionic electronic conductor electrode for symmetrical SOEC that can contribute significantly to simplifying the manufacturing processes. A composite of silver (Ag) and A‐site deficient lanthanum strontium cobalt ferrite ((La0.60Sr0.40)0.95Co0.20Fe0.80O3‐x), is studied for steam electrolysis in a yttria stabilized zirconia electrolyte‐supported symmetrical tubular solid oxide cell. A considerable current density of 250 mA cm−2 is obtained at 1.5 V and 800 °C in a Helium‐Steam atmosphere (50% humidified) with a corresponding polarization resistance as low as 0.15 Ω‐cm2. The polarization resistance is comparable to a number of electrodes reported in the literature for steam electrolysis. However, a 10% drop in current density is observed during the first 20 h of electrolysis at 1.5 V and 800 °C in a Helium‐Steam atmosphere (50% humidified), but no further drop is encountered during the next 46 h of continuous operation.
Performance of symmetrical ferrite‐based fuel electrodes for solid oxide electrolysis applications.
Reversible solid oxide cells (rSOC) enable the efficient cyclic conversion between electrical and chemical energy in the form of fuels and chemicals, thereby providing a pathway for long-term and ...high-capacity energy storage. Amongst the different fuels under investigation, hydrogen, methane, and ammonia have gained immense attention as carbon-neutral energy vectors. Here we have compared the energy efficiency and the energy demand of rSOC based on these three fuels. In the fuel cell mode of operation (energy generation), two different routes have been considered for both methane and ammonia; Routes 1 and 2 involve internal reforming (in the case of methane) or cracking (in the case of ammonia) and external reforming or cracking, respectively. The use of hydrogen as fuel provides the highest round-trip efficiency (62.1%) followed by methane by Route 1 (43.4%), ammonia by Route 2 (41.1%), methane by Route 2 (40.4%), and ammonia by Route 1 (39.2%). The lower efficiency of internal ammonia cracking as opposed to its external counterpart can be attributed to the insufficient catalytic activity and stability of the state-of-the-art fuel electrode materials, which is a major hindrance to the scale-up of this technology. A preliminary cost estimate showed that the price of hydrogen, methane and ammonia produced in SOEC mode would be ~1.91, 3.63, and 0.48 $/kg, respectively. In SOFC mode, the cost of electricity generation using hydrogen, internally reformed methane, and internally cracked ammonia would be ~52.34, 46.30, and 47.11 $/MWh, respectively.
Hydrogen has the potential to play an important role in decarbonising our energy systems. Crucial to achieving this is the ability to produce clean sources of hydrogen using renewable energy sources. ...Currently platinum is commonly used as a hydrogen evolution catalyst, however, the scarcity and expense of platinum is driving the need to develop non-platinum-based catalysts. Here we report a protein-based hydrogen evolution catalyst based on a recombinant silk protein from honeybees and a metal macrocycle, cobalt protoporphyrin (CoPPIX). We enhanced the hydrogen evolution activity three fold compared to the unmodified silk protein by varying the coordinating ligands to the metal centre. Finally, to demonstrate the use of our biological catalyst, we built a proton exchange membrane (PEM) water electrolysis cell using CoPPIX-silk as the hydrogen evolution catalyst that is able to produce hydrogen with a 98% Faradaic efficiency. This represents an exciting advance towards allowing protein-based catalysts to be used in electrolysis cells.
A novel mixed oxide material, Fe-Ce
0.1
Zr
0.9
O
2
-Ag, has been tested as cathode, for the very first time, for one-step methane synthesis in a single temperature solid oxide electrolyser by ...electrolysing a H
2
/CO
2
(4:1 v/v) mixture at 500 °C. Maximum methane selectivity and yield were 6.67 % and 2.66 %, respectively, at an applied potential of 1.6 V (corresponding to a current density of 3.94 mAcm
-2
). CO
2
conversion (~ 40 %) was independent of the applied voltage. However, upon increasing the potential, CO% dropped monotonically with a commensurate increase in methane%. Calculations based on oxide ion removal as a function of current density confirmed that under loaded conditions steam generated in situ (via reverse water gas shift and methanation reactions) got electrolysed to H
2
, which reacted with CO producing more methane. Such excess methane produced purely electrolytically under loaded conditions matched well with the values predicted theoretically assuming that the decrease in CO% was solely due to enhanced methanation.
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