Green hydrogen production from industrial effluent electrolysis: A brief bibliometric analysis and literature review

Renewable energies are gaining ground in the global energy matrix due to their potential to decarbonize the economy. Currently, water electrolysis is one of the main commercial routes used to obtain green hydrogen, and there is a growing interest in alternative water sources to avoid competition between human and animal consumption and fuel production. In this context, a brief bibliometric analysis on "Green hydrogen via effluent electrolysis" was conducted, followed by a literature review aimed at answering the following guiding questions: (i) Are there green hydrogen production systems via effluent electrolysis?; (ii) What renewable energy sources are used by existing systems, and what is their configuration and production scale?; (iii) What electrolysis technologies are used in these systems?; (iv) What are the effluent sources used by existing systems, and what methods are employed for effluent treatment?; (v) What are the applications for hydrogen, oxygen, and residual heat obtained during effluent electrolysis? The results show that: (i) various types of effluent electrolysis systems have been reported; (ii) the main renewable energy source used in these systems is photovoltaic solar energy; (iii) the most commonly used electrolysis technology is the proton exchange membrane type; (iv) the most frequent effluent source is from municipal effluent treatment plants; and (v) the applications of green hydrogen, oxygen, and residual heat can meet the same demands as those of fossil origin hydrogen. Finally, it is evident that research involving effluent electrolysis for green hydrogen production is still in its early stages, indicating a wide field yet to be explored.