Electrochemical CaC₂ -Mediated Conversion of Biochar to C₂ H₂ : High Carbon Efficiency and Low Contamination

The carbon to CaC₂ route is promising to provide a sustainable elementary unit, C₂ H₂ , for the organic synthesis industry, but the traditional thermal reaction process suffers from low carbon efficiency, harmful gas contamination, high temperature operation, and risky CO management. We herein report a high carbon efficiency (ca. 100 %) conversion of biochar to C₂ H₂ through an electrolytic synthesis of solid CaC₂ in molten CaCl₂ /KCl/CaO at 973 K. The main reactions are carbon reduction to CaC₂ at the solid carbon cathode and oxygen evolution at an inert anode. Meanwhile, the electrolysis removes S and P from the solid cathode, avoiding the formation of CaS and Ca₃ P₂ in CaC₂ and consequently eliminating H₂ S and PH₃ contamination in the finally produced C₂ H₂ .