CHROME – Clean Hydrogen Manufacture

There are three main technologies for hydrogen electrolysis, including Polymer Electrolyte Membrane cell (PEM), Alkaline Electrolysis Cell (AEC) and Solid Oxide Electrolyser (SOE). Both PEM and AEC electrolysers are operated commercially, with Alkaline electrolysers being older technology and more widely used in industry, whereas SOEs are still under development and have yet to be commercially deployed. AEC's operate with efficiencies in the range of 70% and the most modern PEM cells have efficiencies up to 82%. AEC electrolysers electrolyse a potassium hydroxide solution, utilise a nickel catalyst and the gasses are separated by a porous membrane whereas PEM electrolysers utilise platinum group metal catalysts which are of limited supply and expensive.

The innovation in CHROME is to operate a hybrid water-splitting process linking the efficient reactors in a typical SMR to the advanced AEC electrolysers with separating the oxidation and reduction chambers for the facile production of green hydrogen. In the oxidation unit, the metal catalyst reacts with water at between 250 to 400C to produce metal oxide, hydrogen, and steam. The oxidised catalyst is separated from the process flow and introduced into the reduction unit, where the oxidised metal catalyst reacts at room temperature with water to produce metal (which is recycled), hydrogen and oxygen.

Experimental data show that the efficiency of CHROME could be up to 25% better than that of the best PEM electrolysers having an efficiency of 94.5% hydrogen conversion with an energy consumption of 3.4kWh per m3 or 42 kWh/kg of Hydrogen. The technology has a low carbon footprint depending on the source of energy supplied and assuming it is powered by offshore wind, the carbon footprint is 20g CO2/kWh, from bio-energy sources, it is 60 to 270g CO2/kWh, and from hydroelectric power, the process footprint is estimated to be between 2-13g CO2/kWh. The process could be developed for both small-scale portable and large-scale stationary applications.

This project will optimise both the oxidation and redox units in terms of process variables, in addition to optimising the recirculating metal catalyst in terms of formulation and physical characteristics. Furthermore, the reduction and hydrothermal processes will be modelled using Aspen plus and COMSOL Multiphysics, respectively. These key data will be used to develop the pilot plant to be constructed and evaluated in a later project and to achieve TRL 7 as an Operational Prototype (Alpha Product).