Upcycling Polyethylene to High-Purity Hydrogen under Ambient Conditions via Mechanocatalysis

Polyethylene (PE) is the most abundant plastic waste, and its conversion to hydrogen (H2) offers a promising route for clean energy generation. However, PE decomposition typically requires high temperatures due to its strong chemical bonds, leading to significant carbon emissions and low H2 selectivity (theoretically less than 75 vol% after accounting for further steam-reforming reactions). Here, we report a mechanocatalytic strategy that upcycles PE into high-purity H2 (99.4 vol%) with an exceptional H2 recovery ratio of 98.5% (versus 15.7% via thermocatalysis), using manganese as a catalyst at a low temperature of 45 °C. This method achieves a reaction rate 3 orders of magnitude higher than thermocatalysis. The marked improvement in H2 recovery ratio is mainly due to metal carbides formation induced by the mechanocatalytic process, which does not catalyze hydrocarbons formation. This work is expected to advance studies of the conversion of polyolefins to high-purity H2 with net-zero carbon emissions.