Renewable sources of energy are becoming more favorable due to the falling prices and the worldwide push for cleaner sources of electricity. However, coal will continue to play a dominant role in global energy mix for at least several more decades. It will be thus imperative to find technologies for efficient utilization of coal with reduced CO2 emissions and facilitate the goal of limiting climate change. In this study, the role of carbon, which can be sourced from coal or biomass has been investigated in the carbon assisted water electrolysis (CAWE) process for hydrogen generation. CAWE process was studied in a PEM-based zero-gap electrolysis cell with continuous circulation of carbon slurry at 70 degrees C by using linear-sweep voltammetry and chronoamperometry techniques. The effect of the addition of electrocatalytic mediators Fe2+ and Fe3+ ions to the carbon slurry was systematically studied on the sustainable current densities. The current densities of up to 52 mA cm(-2) at 1 V have been achieved by the CAWE process in the presence of 100 mM Fe2+ ion additives, and carbon has been demonstrated to contribute to over 30% of the total coulombic charges for the hydrogen production. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.