Sub-volt conversion of activated biochar and water for H2 production near equilibrium via biochar-assisted water electrolysis

초록

Sluggish water oxidation reactions limit water electrolysis for H2 production which can be alleviated by the use of carbon-based materials like agricultural wastes as reducing agents. Biochar from such biomass can reduce equilibrium cell potentials at standard conditions from 1.23 V to 0.21 V by avoiding direct water splitting at the anode. However some challenges hinder biochar oxidation including poor biochar binding electrode caking and surface passivation. We find that enhanced C/O ratio crystallinity and negative zeta potential improve biochar oxidation kinetics at moderate temperatures. Smaller particle sizes and better mixing prevent electrode caking enhancing biochar stability. Here we report sub-volt biochar-coupled H2 production often referred to as a biochar-assisted water electrolysis (BAWE) yielding ∼250 mA/gcat H2 current at 100% Faradaic efficiency. Over 1 mA current was observed at a near-equilibrium cell potential of 0.2 V cell potential. Using a single-junction solar cell-powered BAWE ∼15 mA H2 is generated at 1 Sun resulting in ∼4.8% solar-to-hydrogen efficiency equivalent to ∼35% when the energy of H2 relative to H2O (without biochar) is assumed. © 2024 The Authors

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