Channel electrodes are used to characterize the photochemical DISP2 mechanism in respect of the photoelectro-reductions of (i) 9,10-diphenylanthracene, (ii) benzophenone and (iii) 4-fluorobenzophenone. Quantitative measurements show that the simple DISP2 mechanism requires extension to allow for the possibilities of first a conproportionation step acting as a back-reaction to the disproportionation, and of second quenching of the excited state which leads to reaction. Both these steps, if present, serve to inhibit the overall DISP2 process. Accordingly a general scheme of Self-inhibiting Disproportionation (SID) Mechanisms is introduced and characterized in the channel electrode geometry by computer simulations. A general protocol is established for identifying the various possible sub-cases of the general SID mechanism and illustrated with reference to the three experimental systems of Interest, in all of which both conproportionation and quenching are shown to be mechanistically significant.