(716e) Solar Energy-Driven Biochar-Assisted Electrochemical H2 Production

Hydrogen (H₂) is a promising source of clean energy since it has extreme heat value and eco-environmental advantages. The water electrolysis process is capable of producing high-grade H₂ and it requires 1.23 V cell potential to break water into hydrogen and oxygen molecules, but sluggish water oxidation kinetics result in a high loss of energy, which inhibits its application at the industrial scale. This sluggish kinetic can be improved by co-electrolysis with carbon-based sources such as agricultural wastes. Biochar derived from such wastes is known to drastically reduce the thermodynamic potential of electrolytic H₂ production from 1.23 V to 0.21 V by co-oxidizing biochar and water at the anode and generating protons for H₂ production at the cathode. Therefore, biochar advanced water electrolysis (BAWE) enables the high-value application of biomass with significant energy-saving production of hydrogen as a fuel. The application of BAWE to produce H₂ has several advantages: (i) biochar shows enhanced electrochemical activity than carbon black and graphite; (ii) it is applied at ambient pressure and temperature of >100 ℃ making it different from the conventional gasification process of biochar; (iii) the cathodic and anodic product i.e., H₂ and CO₂, respectively could be further utilized to produce methanol through cascade catalysis system; and (iv) there are several sources of biomass which could be utilized to synthesize biochar for BAWE like animal manure, bagasse, corn stover, etc. In this work, sub-volt H₂ production is demonstrated for the first-time using biochar derived from the chemical dehydration of five different agricultural wastes, such as sugarcane bagasse, paper waste, hemp waste, corn husk, and cow manure. The faradic efficiencies were calculated for the anodic and cathodic products, which were oxygenated hydrocarbons and hydrogen gas, respectively. Using a monocrystalline Si solar cell wired to a biochar-assisted water electrolyzer, a significant amount of current of ~15 mA of H₂ produced was obtained at 1 Sun. Biochar was characterized before and after electrolysis to compare the electrochemical reactivity, efficiency, and durability of the biochar.