In summary, we report the design of a new catalyst based on molybdenum oxycarbide (i.e., MoOxCy) nanosheets with petal-like structures and controlled chemical compositions by PECVD using salts as solid precursors. The plasma-grown, nanoedge-enriched MoOxCy exhibits excellent acidic HER performance with a low overpotential of 415 mV at an ultrahigh current density of up to 10 A cm -2 for 1,000 h. As a result, an ultrahigh H2 throughput of 4,477.4