Bipolar Hydrogen Production from Biomass-Derived Aldehydes and Water in Flow Electrolyzers

It is critical to fight against global warming and confine it to a manageable level of +1.5°C by curbing CO 2 emissions, eventually achieving zero net emissions by 2050. This target will involve significant efforts from all industry sectors and require renewable energy storage and conversion, most of which are heavily rely on clean hydrogen production. Water electrolysis, producing hydrogen and oxygen from water and electricity, is a promising route to the decarbonization of industry and transportation. The main source of energy loss in water electrolysis is the unfavorable thermodynamics (standard potential of 1.23 V vs. NHE) and slow kinetics of oxygen evolution reaction (OER). These challenges motivate us to design efficient paired electrolysis systems to substitute OER. In this work, we demonstrate an efficient bipolar hydrogen production system that combines cathodic hydrogen evolution from water and anodic hydrogen generation from aldehyde oxidation, at a low voltage (~0.1V) with co-generation of high valuable carboxylic acid. We used furfural as the model aldehyde, a biomass-derived compound that is produced on a large scale, currently on a scale of 0.43 million tons/year. Unlike conventional combined systems for hydrogen production that require high voltage (> 1.0 V) and are limited by mass transport (<100 mA cm −2 ) of reactants, this study doubled the hydrogen production rate, obtained industrial-level current density (e.g. 390 mA cm −2 , 0.6V), and achieved economic viability ($2.51/kg of H 2 ). These achievements benefit from a thermodynamically favorable hydrogen production pathway from aldehyde, facile kinetics on porous Cu-based catalysts, efficient mass transport in flow cells, and inexpensive size-exclusive separators. The successful implementation of such an energy-efficient process will impact future low-carbon hydrogen production and distributed chemical manufacturing.