Direct carbon fuel cell (DCFC) technology has the potential to double the electric efficiency and halve the CO2 emissions compared with conventional coal fired power plants. The anode performance, ...long term stability and cell scalability, in addition to fuel feed mechanism, are the major issues for the development of this technology. In this study, lanthanum strontium cobalt ferrite (LSCF) – silver composite anode was evaluated in a scalable version of the DCFC tubular cell in a bed of carbon powder. Ag was added to increase lateral conductivity of the anode and reduce ohmic losses. The cell was operated for 100 h during which it was twice thermally cycled. The performance degradation was studied by employing electrochemical and structural characterisation techniques. The composite anode, in comparison to LSCF anode, produced a 60% improvement in the power density. The sources of performance degradation of the cell were found to be the partial decomposition of the perovskite phase and anode microstructure changes as revealed by XRD and SEM analysis in addition to the loss of carbon contact to the anode resulting from the continuous carbon consumption in the cell.
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•LSCF-Ag composite anodes investigated for direct carbon fuel cell.•Ag addition to anode improved the power densities by 1.5 times.•A scalable tubular cell with LSCF-Ag anode operated in carbon bed for 100 h.•Degradation occurred partly due to anode phase and micro-structural changes.
Low- and intermediate-temperature solid oxide fuel cells (SOFCs) and solid oxide membrane reactors are gaining considerable attention for applications in energy conversion, chemical synthesis, and ...electrolysis. The sluggish oxygen reduction reaction (ORR) causes significant voltage losses for the air electrodes (cathode) in these systems, particularly at lower temperatures (400–600 °C). Surface engineering of electrolytes with nanograined, thin-film interfaces introduced between the cathode and electrolyte is a promising method of reducing the voltage losses associated with ORR on the cathode. In this work, we deposited a nanocrystalline ceria ultrathin film (nanofilm) interface layer on yttria-stabilized zirconia (YSZ) and samaria-doped ceria (SDC) electrolytes using a simple and scalable solution-based deposition process. The effect of the interfacial layers on cathode polarization resistance was studied using impedance spectroscopy and surface imaging techniques. At low temperature (400 °C), the nanofilm interface layer reduced cell polarization resistance substantially for both YSZ and SDC electrolytes. The reduction in the polarization resistance is primarily attributed to the increased interfacial surface area between the platinum electrode and the electrolyte, as confirmed by almost an order of magnitude increase in the interfacial capacitance with nanofilm interface and three-dimensional reconstruction of the surface structures using Confocal Microscopy and Atomic Force Microscopy. The testing of anode-supported thin electrolyte SOFCs at 600 °C clearly demonstrated the benefits of nanofilm interfacial layer in improving the power output of a cell.
The DCFC (direct carbon fuel cell) technology, based on the direct electrochemical oxidation of carbon, has the potential to double the electric efficiency and half the CO2 emissions compared to ...conventional coal fired power plants. In order to assess the scalability of the technology in terms of fabrication and fuel feed system, and to elucidate the possible causes of the cell degradation, a tubular DCFC has been fabricated and operated in a pulverised carbon packed bed at around 800 °C. The cell was operated for a total period of 11 days with many thermal cycles. The electrochemical impedance spectroscopy was used to elucidate the possible causes of the cell degradation. Post-mortem analysis of the cell with SEM (scanning electron microscopy) and XRD (X-ray diffraction) confirmed structural stability of both air and fuel electrodes. A peak power density of 30 mW cm−2 was obtained by direct contact of carbon to the fuel electrode with high purity He as the purge gas. The cell, at the end of operation was still found to produce 60% of the power relative to the power at the beginning of operation, and this study demonstrates the feasibility of continuous operation of the tubular fuel cell in a packed bed of carbon.
•A direct carbon fuel cell was operated for 11 days in a packed carbon bed.•Scalability and continuous operation of fuel cell on solid carbon demonstrated.•MIEC (Mixed ion electronic conducting) anode (LSCF) showed reasonable stability.•Major degradation source is lack of carbon contact with anode as it is consumed.
A complete stand-alone electrolyser system has been constructed as a transportable unit for demonstration of a sustainable energy facility based on hydrogen and a renewable energy source. The ...stand-alone unit is designed to support a polymer electrolyte membrane (PEM) stack operating at up to ∼4
kW input power with a stack efficiency of about 80% based on HHV of hydrogen. It is self-pressurizing and intended for operation initially at a differential pressure of less than 6
bar across the membrane electrode assembly with the hydrogen generation side being at a higher pressure. With a slightly smaller stack, the system has been operated at an off-site facility where it was directly coupled to a 2.4
kW photovoltaic (PV) solar array. Because of its potential use in remote areas, the balance-of-plant operates entirely on 12
V DC power for all monitoring, control and safety requirements. It utilises a separate high-current supply as the main electrolyser input, typically 30–40
V at 100
A from a renewable source such as solar PV or wind. The system has multiple levels of built-in operator and stack safety redundancy. Control and safety systems monitor all flows, levels and temperatures of significance. All fault conditions are failsafe and are duplicated, triggering latching relays which shut the system down. Process indicators monitor several key variables and allow operating limits to be easily adjusted in response to experience of system performance gained in the field.
The conventional electrolysis process for hydrogen generation offers many advantages such as on-site on-demand generation, pure hydrogen that can be stored for latter use directly in fuel cells, and ...potential of direct coupling to a renewable source of energy. However, the process is very energy intensive. Therefore, at present hydrogen is produced mainly by Natural Gas reforming and coal gasification at temperatures in the vicinity of 800 °C. This method of hydrogen production involves the steps of reforming/gasification, shift reaction and gas separation at high temperatures to improve hydrogen yield and purity based on its application. This paper investigates the thermodynamic and practical energy benefits of single step water electrolysis process assisted by carbon, where part of the energy can come from the chemical energy of carbon. The process has been demonstrated in a solid state electrolytic cell operating at near room temperature. The paper also discusses the technology status and challenges to achieve high hydrogen generation rates.
•H2 generation by carbon assisted electrolysis requires 60% less electric input.•Feasibility of solid electrolyte based carbon assisted electrolysis demonstrated.•Process emulates H2 generation via coal gasification employing multiple reactors.•Process offers high economic viability if further coupled to renewable power.
Direct carbon fuel cells offer twice the efficiency compared with conventional coal-fired power plants and the highest efficiency among various fuel cells. However, the delivery of solid fuel to ...electrode/electrolyte interface is a critical issue and hinders the long-term performance of the fuel cell. The use of mixed ionic electronic conducting anodes has the potential to reduce the problem by shifting the fuel oxidation reaction from anode/electrolyte to anode/solid carbon interface. In search for a better anode material, Y
2
O
3
-doped ceria has been investigated as a suitable anode material for use in direct carbon fuel cells and the performance compared with Gd
2
O
3
-doped ceria. These materials have high ionic conductivity in oxidizing environments and are also known to have reasonable mixed ionic and electronic conductivity in reducing environments. In this manuscript, the stability of the anode materials in fuel cell operating environments has been investigated with X-ray diffraction (XRD) and scanning electron microscopy. Electrochemical impedance spectroscopy, in pure N
2
and CO
2
/N
2
anode chamber atmospheres, has been used to deconvolute the contribution of various fuel cell components to voltage losses and to elucidate the reaction mechanism. No precious metals were used on the anode side, neither as a catalyst nor as a current collector.
For power generation, fuel cells offer a number of advantages over conventional thermal power stations such as high efficiency, low pollution and CO2 emissions and the ability to be used as ...distributed power generation sources at load centres. Amongst these, the direct carbon fuel cell (DCFC) offers many additional attributes which include near 100% fuel utilisation, 100% theoretical efficiency and almost pure CO2 in the flue stream requiring no costly separation from other gases. In the solid oxide electrolyte based DCFC, for effective oxidation of solid fuel, the anode plays a significant role. In particular, the mixed ionic electronic conducting ceramics offer the potential of shifting reaction sites from anode/electrolyte interface to fuel/anode interface thus making it easier for oxidation of solid fuel which unlike gaseous fuels cannot penetrate in the porous structure of the anode. In this paper, in view of a good mix of ionic and electronic conductivity and the possibility of higher catalytic activity of Co doped lanthanum strontium titanates for hydrocarbon fuel oxidation, these materials have been investigated as a potential anode for use in a DCFC. The performance was evaluated with solid carbon, H2 and CO as fuel feeds. The performance has been compared with Sr0.86Y0.08TiO3 and La0.3Sr0.7TiO3. The effect of adding a noble metal catalyst in small quantities has also been reported to facilitate the carbon oxidation reaction.
The optimal utilisation of fuels such as hydrogen and methanol in micro fuel cells (MFC) in combination with effective fuel storage solutions can offer much longer operational and standby time and ...shorter recharging time compared to batteries. Therefore, MFCs have an immense potential to replace or to be used in combination with batteries for portable power applications. However, the overall fuel cell system is required to be compact to suit the appliance, have a simple support system, manufacturable at a mass scale with low cost materials and fabrication technologies, and have lifetimes significantly longer than batteries. In a fuel cell stack, the interconnect plates occupy majority of the volume of the stack, and reducing their size (thickness) and weight would be enormously beneficial in terms of improving the power density of the device. Therefore, the purpose of this study is to investigate design options of the interconnect plate for operation of the stack under ambient and passive conditions. Three stacks (power output in the 3–12 We range) were built using two designs and lifetime tests were performed up to 21,000 h using industrial grade hydrogen under both constant and simulated cyclic loads. The voltage–current characteristics of the stacks were analysed by model equations and the overall performance was assessed by performing energy balance calculations. The major source of cell degradation, increasing amplitude of voltage fluctuations and manifestation of limiting current behaviour for some cells have been discussed and appear to be related to the poisoning of Pt catalyst by impurities such as S, Hg and CO present in the industrial grade hydrogen used in the study, leading to increasing loss of electrochemical active surface area of the catalyst with time.
► Bipolar plate design for self air breathing micro fuel cell has been discussed. ► Fuel cells tested up to 21,000 h with simple BOP and industrial grade hydrogen. ► Impurities in H2 increase cell degradation and amplitude of voltage fluctuations. ► Appearance of limiting current with time for some cells in a stack was observed. ► Fuel cell performance was assessed through energy balance calculations.
Oxygen is required for treatment of patients in hospitals and at home, in industrial processes and for fuel combustion. Most commonly oxygen is produced by cryogenic or pressure swing adsorption ...routes. Other techniques include oxygen-ion conducting ceramic membranes, polymer membranes and chemical processes used mainly in civil aviation to reduce the condition of hypoxia at high altitudes. Water electrolysis is used mainly for the production of hydrogen with oxygen as a by-product. In order to use this system only for oxygen production, hydrogen must be utilised and disposed off safely. This, however, is not practical in many instances where there is no use for hydrogen and it poses an explosion hazard. In this paper, an electrolyser system based on polymer electrolyte membrane is described in which hydrogen produced on one side of the electrochemical cell is consumed by combining it with atmospheric oxygen, through operating the cell in a carefully configured fuel cell mode. This reduces the power consumed in the electrolysis operation by more than 35% and eliminates hydrogen in exit gases. Oxygen generated is of high quality and can be used for human consumption (portable and plug-in home care oxygen therapy devices, in hospitals, defence or aerospace requirements) and for many other industrial applications.
There is an ever – increasing demand for more powerful, compact and longer – life power modules for portable electronic devices for leisure, communication and computing. Micro fuel cells have the ...potential to replace battery packs for portable electronic appliances because of their high power density, longer operating and standby times, and substantially shorter recharging times. However, fuel cells have stringent operating requirements, including no fuel leakage, water formed in the electrochemical reactions, heat dissipation, robustness, easy and safe use, and reliability. Due to the large market potential, several companies are currently involved in the development of micro fuel cells. For application of fuel cells as a battery charger or in a battery replacement market, the cells require simplification in terms of their construction and operation and must have volumetric power densities equivalent to or better than those of existing battery power packs. This paper discusses results of investigation on methods and materials for direct hydrogen micro fuel cells as well as the lifetime performance of single cells and 2 W
e arrays. The paper also reviews the global technology development status for the direct hydrogen micro fuel cell and compares its salient features with other types of micro fuel cells.
