Hydrogen production and solar energy storage with thermo-electrochemically enhanced steam methane reforming.

Hydrogen is widely regarded as a sustainable energy carrier with tremendous potential for low-carbon energy transition. Solar photovoltaic-driven water electrolysis (PV-E) is a clean and sustainable approach of hydrogen production, but with major barriers of high hydrogen production costs and limited capacity. Steam methane reforming (SMR), the state-of-the-art means of hydrogen production, has yet to overcome key obstacles of high reaction temperature and CO emission for sustainability. This work proposes a solar thermo-electrochemical SMR approach, in which solar-driven mid/low-temperature SMR is combined with electrochemical H separation and in-situ CO capture. The feasibility of this method is verified experimentally, achieving an average methane conversion of 96.8% at a dramatically reduced reforming temperature of 400-500 °C. The underlying mechanisms of this method are revealed by an experimentally calibrated model, which is further employed to predict its performance for thermo-electrochemical hydrogen production. Simulation results show that a net solar-to-H efficiency of 26.25% could be obtained at 500 °C, which is over 11 percentage points higher than that of PV-E; the first-law thermodynamic efficiency reaches up to 63.27% correspondingly. The enhanced efficiency also leads to decreased fuel consumption and lower CO emission of the proposed solar-driven SMR system. Such complementary conversion of solar PV electricity, solar thermal energy, and low-carbon fuel provides a synergistic and efficient means of sustainable H production with potentially long-term solar energy storage on a vast scale.