Simulation of the medium- and long-term development of China's hydrogen energy industry and policy impacts

China's hydrogen supply structure remains heavily dependent on fossil fuels, making the promotion of green and low-carbon development in the hydrogen energy industry (HEI) critical for achieving national dual-carbon targets. This study forecasts future trends in China's HEI and explores policy pathways to support its sustainable development. To this end, a system dynamics (SD) model is developed to analyze the medium- and long-term development of China's HEI. The model captures hydrogen production from both fossil-based and renewable sources, while also accounting for carbon emissions from the gray hydrogen sector, and systematically evaluates the impacts of relevant policy interventions. The results indicate that: (1) Under the current development trajectory, green hydrogen production is projected to reach 7.5335 million tonnes (Mt) by 2035, with alkaline water electrolysis remaining the dominant technology. (2) In the absence of policy constraints, gray hydrogen production is expected to peak at 34.5072 Mt in 2034, with associated carbon emissions of 678.2689 Mt, and coal-based hydrogen remaining the primary source. (3) Unit subsidies for green hydrogen, tax incentives, and capacity replacement policies are more effective in promoting green hydrogen development than fixed asset investment subsidies and technological progress alone. (4) Capacity replacement and reduction policies accelerate the timing of peak fossil-based hydrogen production and reduce peak levels, while carbon pricing mechanisms exert stronger effects in constraining high-carbon pathways.