A Na-ion direct formate fuel cell converting solar fuel to electricity and hydrogen

The rapid footstep of hydrogen society drives people to pursue the reliable, energy-saving, and renewable hydrogen production patterns. Herein, an electricity-hydrogen co-produced Na-ion direct formate fuel cell (e-h₂ Na-DFFC) is proposed as a conceptual avenue to link the CO₂ utilization and H₂ society. Using the solar fuel-formate that can be readily synthetized from carbon dioxide, we experimentally demonstrate the capability of e-h₂ Na-DFFC for continuous co-production of electricity and hydrogen. A proof-of-concept e-h₂ Na-DFFC yields a peak power density as high as 168 mW cm⁻² at 380 mA cm⁻² associating with the hydrogen production rate reaching 2.9 mL min⁻¹ cm⁻². More importantly, the approximate 100% purity and over 98.9% Faradic efficiency suggest the great potential of this electricity-hydrogen co-production device. In addition, we explore the scalability, stability and applicability of the e-h₂ Na-DFFC. The hydrogen that is produced from the e-h₂ Na-DFFC can be directly fed to hydrogen-oxygen fuel cell, which presents a peak power density of 546 mW cm⁻² and a 35-h stable operation at room temperature. This proposed e-h₂ Na-DFFC provides a new pathway for renewable hydrogen production.