Coupling Hydrogen Production and Upgrading of Chemicals in Oxide-Based Photoelectrochemical Device

Green H₂ has been recognized as an important element in efforts to decarbonize our fossil fuel-dependent society. One method to produce green H₂ is solar water splitting in a photoelectrochemical (PEC) device. Solar-to-hydrogen (STH) efficiencies of up to 30% have been demonstrated but these high efficiencies could only be achieved using expensive and non-scalable photoelectrodes–the approach therefore still results in a hydrogen cost that is not competitive. One obvious approach is to develop novel photoelectrode materials that are low-cost and highly efficient. For example, earth-abundant complex metal oxides have been explored, and several promising ones have been identified. Here, our efforts in developing tin tungstate (α-SnWO₄) as a photoelectrode material will be discussed.[1-3] Alternatively, co-production of valuable chemicals can be introduced in the PEC cell to increase the competitiveness of the overall system. For example, we recently coupled a homogeneous hydrogenation reaction with PEC-generated hydrogen inside a single device.[4,5] Using the hydrogenation of itaconic acid (IA) to methyl succinic acid (MSA) as a model proof-of-concept reaction, solar-driven H₂-to-MSA conversion as high as ~50% was demonstrated using our BiVO₄-based PEC device. Although still demonstrated in the laboratory scale, life-cycle net energy assessment and technoeconomic analysis reveal that the concept indeed offers a very promising return. Finally, further implications and optimization potentials of this coupled PEC hydrogenation approach, also beyond the demonstrated hydrogenation of IA to MSA, will be discussed.<br/><br/>References<br/>1. P. Schnell et al. <i>Adv. Energy Mater. </i>11, 2021, 2003183<br/>2. P. Schnell et al., <i>Chem. Mater. </i>34, 2022, 1590<br/>3. P. Schnell et al. <i>Solar RRL </i>7, 2023, 2201104<br/>4. X. Zhang et al. <i>Nat. Commun. </i>14, 2023, 991<br/>5. K. Obata et al. <i>Nat. Commun. </i>14, 2023, 6017