Solar Thermal Electrochemical Process (STEP) action to biomass: Solar thermo-coupled electrochemical synergy for efficient breaking of biomass to biofuels and hydrogen

Highlights: • The solar action to biomass was proposed for "breaking" the biomass to fuels. • The breaking temperature was greatly lowered via solar thermolysis plus electrolysis. • The solar chemical process achieved a high solar utilization and biomass conversion. • The mechanism can be revealed by the thermo/electro-induced free radical reactions. • The process features a renewable and sustainable system of solar and biomass to fuel. -- Abstract: In this paper, secondary solar action to biomass, focused on the conceptualized intersection of solar energy and biomass, is presented to illustrate how "breaking" of biomass to biofuels plus hydrogen can be utilized for the adaptation of Solar Thermal Electrochemical Process (STEP) chemistry. This Solar Thermal Electrochemical Process (STEP) system was designed and employed for the synergetic solar energy and corresponding chemistry to provide an action of biomass for efficient solar and biomass utilization - production of biofuels plus hydrogen. The control and modulation of solar fields and sub-chemical reactions were adopted to achieve a high utilization of solar energy, high chemical conversion rate, and high selectivity of the biomass to achieve rich biofuels and abundant hydrogen. The Solar Thermal Electrochemical Process (STEP) temperature of the breakdown reaction was greatly lowered by using electrolysis, as compared with the conventional pyrolysis. Based on their structural complexity and thermal stability, cellulose and lignin are well-suited for the production of biofuel and hydrogen. Through the coupling of thermolysis and electrolysis, the Solar Thermal Electrochemical Process (STEP) hydrogen production from cellulose was 7.2 times higher under a current of 100 mA and 8.8 times higher at 400 mA compared with pyrolysis at 200 °C. The Solar Thermal Electrochemical Process (STEP) lignin conversions were significantly improved by reaching 87.22%, 21.78%, 57.72%, and 7.22% (340 °C, 400 mA), while the pyrolysis achieved only 52.39%, 19.48%, 25.81%, and 7.10% (340 °C, 0 mA), respectively, for the total rate, solid, liquid, and gas fractions. With electrochemical synergy to help, the Solar Thermal Electrochemical Process (STEP) process efficiently and selectively produced gas hydrocarbons, liquid biofuel, and hydrogen. The light hydrocarbons in the gas phase, such as methane, ethane, and n-pentane, became more abundant via thermo-electrolysis. The Solar Thermal Electrochemical Process (STEP) chemistry for converting biomass to biofuels and hydrogen was also elucidated in this paper. The simplified mechanism can best be described by a series of thermo/electro-induced free radical reactions. The system, built on solar energy and specific chemical reactions, features a perfect, green, sustainable, and recyclable operation to transform solar biomass to biofuels and hydrogen.