Coupling pretreatment of lignocellulosic biomass for enzymatic hydrolysis with electrochemical reduction of CO₂ for production of formic acid

A new coupled electrolysis system has been developed by combining pretreatment of lignocellulosic biomass (corn stover) in alkaline anolyte for increasing cellulose digestibility with electrochemical reduction of CO₂ on the cathode to produce formic acid. Electrodeposition of Sn on calcinated copper foam results in preparation of an efficient cathode, ED-Sn@CuO_x, achieving 83.2% Faradaic efficiency of formate formation with a current density of 69.2 mA cm^-2 in an H-type electrolysis cell. The ferricyanide/ferrocyanide redox couple plays an efficient electron mediator to improve the rate of electron transfer. Oxygen evolution reaction can be significantly suppressed, increasing the production rate of formate. Corn stover can be simultaneously pretreated by delignification in alkaline anolyte. Under the relatively optimal condition, the pretreated substrates obtained 96.6% glucose yield and 83.4% xylose yield. By inputting 1 kWh of electricity, the coupled system can obtain 0.27 kg formate with simultaneously pretreating 31.1 kg corn stover, resulting in the production of 14.2 kg fermentable sugars by subsequent enzymatic hydrolysis. Meanwhile, alkaline delignification in the anolyte also plays an important role in the increase of the pretreatment efficiency.