Steering the adsorption modes and oxidation state of Co oxyhydroxide active sites to unlock selective glucose oxidation to formate for efficient solar reforming of biomass to green hydrogen

One solution to the intermittency of renewable energy sources is energy storage in fuels such as hydrogen produced by water electrolysis. However, current water electrolysis systems are plagued by high costs. Here, a co-electrolysis system for biomass-derived glucose and water is shown to achieve green hydrogen generation of over 500 μmol h –1 cm –2 using a membrane-free undivided cell with electrocatalysts comprising only earth-abundant elements, driven by a triple-junction photovoltaic. Glucose is selectively electrooxidized to formate with high yields of up to 80%, instead of water being oxidized into oxygen; the former circumvents the need for costly membranes to separate the hydrogen and oxygen gaseous products. High selectivity is achieved through cascade carbon–carbon bond oxidation by regulating the adsorption mode and moderating the oxidation state of cobalt with copper doping. The overall electrolysis potential is lowered by ∼400 mV compared to water splitting. The revenue from the formate co-product can lower the levelized cost of hydrogen from water electrolysis by $4.63/kg of hydrogen produced, making it competitive with grey hydrogen generation.