This paper provides a status update on the high-temperature electrolysis (HTE) research and development programme at Idaho National Laboratory (INL), with an overview of recent large-scale system modelling results and the status of the experimental programme. System analysis results have been obtained using the commercial code UniSim, augmented with a custom high-temperature electrolyser module. The process flow diagrams for the system simulations include an advanced nuclear reactor as a source of high-temperature process heat, a power cycle and a coupled steam electrolysis loop. Several reactor types and power cycles have been considered, over a range of reactor coolant outlet temperatures.

High-temperature steam electrolysis (HTSE) coupled with nuclear energy is one of the most promising options for hydrogen mass production. CEA (the French Atomic Energy Commission) is carrying out research in this field, from materials, cells and components developments to stack design including components and stack testing.

Emphasis on energy security issues has brought much-needed attention to economic production of hydrogen as the secondary energy carrier for non-electrical markets as well as to meet increasing demand for crude upgrading and desulphurisation. While steam reforming of methane is the current method of production of hydrogen, the fossil fuel feed consumes non-renewable fuel while emitting greenhouse gases. Thus, in the long run, efficient, environmentally-friendly and economic means of hydrogen production using nuclear and renewable energy needs to be developed. Steam electrolysis, particularly using high temperature ceramic membrane processes, provides an attractive option for efficient generation of high purity hydrogen.

Gas tightness over a long period of time is a real challenge in high-temperature electrolysis. The seals must indeed be able to run at high temperature between metals and brittle ceramic materials, which is a major issue to be solved. The common sealing solution relies on glass-made seals, despite their low mechanical strength at high temperature. Metallic seals have seldom been used in this field, because their stiffness and their hardness require a much higher load to achieve the appropriate tightness.

High temperature steam electrolysis is one of the most efficient processes for hydrogen generation from water with no CO2 emissions using electricity and heat from nuclear or concentrated solar plants. Solid Oxide Electrolytic Cells (SOEC) are the proposed technology being researched and developed for this purpose. Over a long period of operation of the cells, various sources for degradation in the cells’ electrochemical performance prevail, and hence the cell resistance increases and the process becomes inefficient. Our research is aimed at identifying the mechanisms for the loss in the electrochemical performance of the cell, particularly of the oxygen electrode, namely the anode.

Steam electrolysis experiments conducted at Idaho National Laboratory (INL) have demonstrated an efficient process to generate hydrogen using waste heat and electricity from a nuclear power plant. However, the hydrogen output was observed to decrease significantly over time. Solid oxide stack components from the INL studies were analysed at Argonne National Laboratory to elucidate the degradation mechanisms of electrolysis. After probable regions of degradation were identified by surface techniques, Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to further characterise the causes of degradation by examining cross-sections of stack components.

In a carbon-dioxide-constrained world, the primary methods to produce electricity (nuclear, solar, wind and fossil fuels with carbon sequestration) have low operating costs and high capital costs. To minimise the cost of electricity, these plants must operate at maximum capacity; however, the electrical outputs do not match changing electricity demands with time. A system to produce intermediate and peak electricity is described that uses light water reactors (LWR) and high temperature electrolysis. At times of low electricity demand the LWR provides steam and electricity to a high temperature steam electrolysis system to produce hydrogen and oxygen that are stored. At times of high electricity demand, the reactor produces electricity for the electrical grid. Additional peak electricity is produced by combining the hydrogen and oxygen by operating the high temperature electrolysis units in reverse as fuel cells or using an oxy-hydrogen steam cycle. The storage and use of hydrogen and oxygen for intermediate and peak power production reduces the capital cost, increases the efficiency of the peak power production systems, and enables nuclear energy to be used to meet daily, weekly and seasonal changes in electrical demand. The economic viability is based on the higher electricity prices paid for peak-load electricity.