A ternary system exploiting the full solar spectrum to generate renewable hydrogen from a waste biomass feedstock

A solar-driven system is proposed capable of hydrogen production from waste biomass with low carbon and water footprints. The ternary system consists of a membrane-based waste biomass concentrator (WBC), a biomass preconditioning reactor (BPR) integrated with an array of hybrid PV-thermal (PVT) collectors, and a flow electrolysis cell (FEC) equipped with a custom, high-performance electrode – NiMo alloy deposited onto Ni foam. An innovative full-solar-spectrum hybrid PVT reflector-concentrator was constructed to confirm performance; this enabled a thermal efficiency of up to ∼50% to be achieved when operating the BPR at 120–150 °C, while also converting ∼8% of the solar flux to electricity for the FEC. The solar-thermal BPR can reform recovered waste biomass (i.e., a sugar-containing liquid feedstock) into a bio-alcohol (5-hydroxymethylfurfural) with a yield of 25 mol%, with the transformed biomass then used to feed the anodic compartment of the FEC. Within the FEC, biomass electrolysis using the NiMo catalyst facilitated hydrogen production, offering a low energy consumption of 40–53 kW h kg⁻¹, which is 16–28% more efficient than alkaline water splitting using Ni foam electrodes. The ternary system achieved a 7.5% overall solar-to-hydrogen efficiency, additional revenue from clean water production (with >80% water reclaimed), and a value-added chemical by-product (2,5-furandicarboxylic acid at a 3–10% yield from the waste sugar stream). This work presents a new route towards efficient and economically feasible renewable hydrogen production—a system which can underpin a circular economy.