Light-driven water-splitting to generate hydrogen and oxygen from water is typically
carried out in an electrochemical cell with an external voltage greater than 1.23 V applied between
the electrodes. In this work, we examined the use of a concentration/chemical bias as a means of
facilitating water-splitting under light illumination without the need for such an externally applied
voltage. Such a concentration bias was created by employing a pH differential in the liquid electrolytes
within the O2-generating anode half-cell and the H2-generating cathode half-cell. A novel, stretchable,
highly ion-conductive polyacrylamide CsCl hydrogel was developed to connect the two half-cells.
The key feature of the cell was the half-cell electrodes, which comprised thin-film conducting polymer
composites that were previously designed to maximize light-driven catalysis at moderate pH. Upon
being connected with the hydrogel in the presence of light irradiation (0.25 sun intensity on each
electrode), the half-cells spontaneously produced hydrogen and oxygen from water, without the need
for an externally applied voltage bias greater than 1.23 V. The cell operated reliably and efficiently
for 14 h of continuous testing. These results demonstrate the fundamental feasibility of light-driven
water-splitting in a photoelectrochemical concentration cell when employing electrodes that operate
efficiently at moderate pH, even with low levels of light illumination. The designed conducting
polymer composites proved ideal in that regard.