Until now, we have explored the photocurrent response of either a PA or a PB in a single-cell configuration. We suggested that due to the interaction of ions (formed upon the irradiation) with the interface, the rate of reaction could be modified. In this context, pH is an important factor. To explore the effect of pH, we introduce in this section a different design of a photoelectrochemical cell, which is an H-type cell made of glass with 2 quartz optical windows, separated by a Nafion membrane (Figure ). Before describing the electrochemical measurements, we used this configuration without the electrodes, while having the 2N6S PA and 6AQ PB in separate cells, to explore the proton transfer between the two half-cells. As before, upon light irradiation, the 2N6S will result in proton dissociation and 6AQ will result in proton association. One of the challenges in using Brønsted PA and PB is the competition with the proton recombination process, meaning the return of the proton to the PA or the deprotonation of the PB upon returning to their ground state. In some cases, other processes can influence this recombination, such as proton transfer to/from another proton acceptor/donor that is not water. In our study, the participation of the formed ions (RO -/H + /RNH + ) in the electrochemical process competes with the recombination process. In this section, in the absence of the electrochemical setup, we are targeting the ability of the Nafion membrane to capture and pump protons from one half-cell to the other, which also competes with the recombination process. To explore this, we have used the H-cell configuration while measuring the concentration of protons, i.e., the pH of the solution, in each half-cell. While placing the pH electrode in the half-cell containing the 6AQ PB, a pH increase was measured upon irradiation of 2N6S that continued also in dark, while only upon irradiation of the 6AQ, a decrease in the pH was observed that also continued in the dark until the start of the next cycle (Figure ). The opposite trend was obtained while placing the pH electrode in the half-cell containing the 2N6S PA, where the pH decreased upon irradiation of 2N6S and continued to decrease in dark, while upon irradiation of 6AQ, the pH increased and continued to increase in dark (Figure ). The mirror image of the two independent experiments indicates a proton transport through the Nafion membrane of the H-cell, resulting in a light-induced modulation of the pH by switching the irradiation between 2N6S and 6AQ. To explain these results, we suggest the following mechanism (Figure ): (I) First, PA is present in the CE compartment in its protonated form (ROH), while PB is present in its deprotonated form (RN) in the WE compartment. The compartments are separated by Nafion membrane, composed of a hydrophobic tetrafluoroethylene backbone with pending ether groups terminated with sulfonate groups. As shown in previous studies of Nafion, the sulfonic groups are present both in their protonated and deprotonated states. (II) Upon the irradiation of the CE compartment, RO -ions are formed in the excited state, followed by a recombination in the ground state. Far from the Nafion membrane, this H + recombination will be from the bulk water solution. However, adjacent to the membrane interface, the RO -ions can recombine with H + coming from the sulfonic groups, hence, deprotonate them. This, in turn, will induce a cascade of proton transfer reactions that will eventually deprotonate some of the water molecules on the other side of the membrane, thus, generating a proton flux from the WE towards the CE compartment. (III) Following proton transport from one side of the membrane to another, the CE compartment becomes more acidic, while the WE compartment becomes more basic. (IV) Upon the irradiation of the WE compartment, the PB molecules in their excited state (RN * ) act as strong bases and they can abstract protons from a proton donor. Away from the membrane, water acts as the donor. However, next to the membrane interface, the sulfonic groups can act as proton donors. As above, this will induce a cascade of proton transfer reactions that will eventually abstract protons from the solution on the other side of the membrane, thus, generating proton flux from the CE towards the WE compartment. Accordingly, the pH in the WE and CE compartments drops and rises back again, respectively, to its initial value.