There is a growing interest in the nanostructure of metal nanoparticles encapsulated in carbon shells (M/C) to act as cost-effective and high-performance electrocatalysts for hydrogen production. Despite tremendous efforts, large-scale and controllable production of highly-active M/C nanocomposites for electrocatalysis remains a great challenge. Herein, we report a tunable and general strategy tandem plasma reaction (TPR) for manufacturing a series of carbon encapsulated Ni/C nanocomposites with different compositions. Benefiting from the synergistic effect between the conductive carbon layer and Ni nanoparticles, the electrocatalytic performance can be adjusted to an optimal state. A volcano shape dependence between electrocatalytic activity and the percentage of carbon is presented experimentally. With the simplicity and intelligence of the approach, the strategy based on tandem plasma reaction presents great potential to the preparation of extendable metal/carbon nanocomposites for versatile applications. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.