A comprehensive review of carbon and hydrocarbon assisted water electrolysis for hydrogen production

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.