Green hydrogen: A holistic review covering life cycle assessment, environmental impacts, and color analysis

The urgency of addressing climate change, energy security, and ecological concerns has driven the global shift towards renewable energy systems. In this transformative era, green hydrogen emerges as a pivotal energy resource, promising substantial reductions in global emissions. Methods like water electrolysis, biomass gasification, and methane reforming with carbon capture and storage offer pathways to synthesize hydrogen without greenhouse gas emissions. Currently, hydrogen accounts for approximately 4% of global energy generation, with projections suggesting this could increase to 10% by 2030 and 20% by 2050. Integrating nuclear energy into hydrogen production presents a low-carbon option, promoting reliability and meeting growing demand across sectors. For instance, incorporating nuclear energy could reduce emissions by up to 90% compared to conventional methods. Categorizing hydrogen production into colors based on emissions provides a framework for understanding their environmental and socio-economic profiles. For example, green hydrogen can reduce lifecycle emissions by 60-90% compared to gray hydrogen. Life cycle analysis aids in evaluating overall impacts, guiding policy formulation and industrial decisions towards sustainability. This review examines various production pathways, highlighting their potential contributions to a carbon-neutral economy and discussing the hydrogen spectrum's role in characterizing production processes based on carbon emissions.