Life cycle assessment of alternatives for hydrogen production from renewable and fossil sources

New processes under development for producing hydrogen have been assessed using a life cycle methodology and compared to conventional ones. The aim of this paper is to determine the main obstacles to be beaten or the critical aspects to be addressed to ensure the feasibility of these processes. Water photosplitting, solar two-step thermochemical cycles and automaintained methane decomposition with different lay-outs were studied. They have been compared to methane steam reforming with CCS and electrolysis with different electricity sources. The results show the good behaviour of the automaintained methane decomposition. This process is one of the best options when the greenhouse effect emissions are evaluated. Nevertheless, the consumption of a great amount of a non-renewable resource, i.e., natural gas, as reagent can be negative. The two-step thermochemical cycles based on NiFe₂O₄ is also an interesting option, but its behaviour depends largely on the infrastructure materials employed on the installations. The most promising option is photosplitting with CdS as catalysts. This process shows the best performance.