Photoelectrochemical visible light zero-bias hydrogen generation with membrane-based cells designed for decreasing overall water electrolysis voltage and water dissociation: the second stage

Abstract

We created a two-compartment cell (2CC) separated by a bipolar membrane (BPM) sandwiched between a through-holed (TH) electrode assembly (BPMTHEA-2CC) with the distinguishing feature of integrated functionality of dualities based on the Golden Rule for sustainable water splitting derived from water dissociation (WD) with a dual chemical bias (CB). A decisive advantage of this system is that all electrolytes used are sustainable because the reaction starts from WD. The opposite bidirectional charge separation of H+ and OH− ions derived from WD generates inner CB within BPM. Many anolyte–catholyte combinations are possible in BPMTHEA-2CC, which induces outer CB (OCB). Therefore, dual CB reduces overall water electrolysis voltage. We have achieved hydrogen generation derived from WD with BPMTHEA-2CC using an oxygen evolving reaction active TH dimensionally stable anode by imposing a voltage with less than the theoretical 1.23 V for water splitting at room temperature. We disprove the theory of water electrolysis established for hundreds of years. Instead of external voltage, we have harnessed solar energy by applying the TH n-type semiconductor photoanodes to BPMTHEA-2CC for a zero-bias photogalvanic cell. Anatase TH TiO2 was used for a model to demonstrate our concept. We succeeded in measuring photocurrent from distilled water with a response of optical shutter. The magnitude of the zero-bias photocurrent is proportional to the magnitude of OCB and illuminance intensity. TH Fe2O3 was prepared by the aqueous chemical growth method. Visible light zero-bias photocurrent from distilled water was also observed in the TH Fe2O3 photogalvanic cell without any external voltage.