Hydrogen Generation Coupling with High-Selectivity Electrocatalytic Glycerol Valorization into Formate in an Acid-Alkali Dual-Electrolyte Flow Electrolyzer

Owing to its high energy density , sustainability, and pollutionfree combustion, hydrogen is considered one of the most promising emerging energy carriers to replace conventional fossil fuels . Among the various hydrogen production technologies, electrolytic water splitting has gained significant attention thanks to its high efficiency and environmentally friendly characteristics. However, the large-scale application of electrolytic water splitting is often hindered by the limitations imposed by the anodic oxygen evolution reaction (OER). To overcome this challenge, a promising alternative approach is to replace the OER with the electrocatalytic glycerol oxidation reaction (GOR) at the anode. This substitution can lead to energy savings and enhanced efficiency of electrolytic water splitting for hydrogen production , thereby further promoting the development of hydrogen as a clean energy source. However, the application of the GOR at anode requires efficient, cost-effective, and highly selective electrocatalysts . To this end, we report the development of a novel acid-alkaline dual-electrolyte flow electrolyzer (AADEF-electrolyzer) by coupling the GOR at the alkaline anode with the hydrogen evolution reaction (HER) at the acidic cathode. A self-supported NiCo 2 O 4 nanoneedle electrode material (NiCo 2 O 4 /NF) has been in situ grown on nickel foam (NF) using a simple hydrothermal-calcination method. The electrode demonstrates excellent electrocatalytic performance for the GOR, achieving high electrolysis current density at low potentials and exhibiting high selectivity for formate production, with the Faraday efficiency exceeding 85%. Density functional theory (DFT) calculations imply that NiCo 2 O 4 has a lower energy barrier for the reaction and that the presence of Ni facilitates the reduction of the Co state density, thereby promoting the GOR. An innovative AADEF-electrolyzer was constructed by utilizing NiCo 2 O 4 /NF as the anode for the GOR and an acidic cathode for the HER. Experimental results indicate that the AADEF-electrolyzer exhibits excellent GOR performance with a low overpotential and high selectivity toward formate production. It requires a voltage of only 0.36 V to achieve a current density of 10 mA·cm −2 and long-term stability with a Faraday efficiency close to 100% for hydrogen production. The low-cost and easily fabricated self-supported electrode material, together with the acid–alkaline dual-electrolyte flow electrolyzer, provide an innovative strategy for developing hybrid electrolysis systems.