Proton coupled electron transfer from Co₃O₄ nanoparticles to photogenerated Ru(bpy)₃³⁺: base catalysis and buffer effect

Abstract

Flash photolysis studies indicate general base catalysis by borate in photoinduced proton-coupled electron transfer from Co3O4 nanoparticles to Ru(iii)(bpy)33+.

Mechanistic Insights into Light‐Activated Catalysis for Water Oxidation

“…Concerning electron transfer from the WOC to PS + (hole scavenging), this is also expected to be accelerated in a photoelectrode, since it shifts from a bimolecular event in the EA/PS/WOC system (µs‐ms timescale, see paragraph 3) to unimolecular ones, expected in ps‐ns timescale. Nonetheless, the investigation of the hole scavenging process in the EA/PS/WOC system may reveal if significant activation barriers are associated to the WOC activation (as in the case of IrO x , where slow ET to photogenerated Ru(III) oxidant occurs both in the sacrificial system and at a photoanode, ), or if external additives may enhance the electron transfer rate (as in the case of Co 3 O 4 nanoparticles, where a base from the buffer enhances the rate of a proton coupled electron transfer to Ru(III) oxidant) . Other associated information from the ET in the EA/PS/WOC system deal with the number of ET from the WOC in a fixed timescale (typically ca 100 ms), and in the ET kinetic analysis of active intermediates of the WOC …”

“…Interestingly, a detailed investigation of the electron transfer process from Co 3 O 4 nanoparticles to photogenerated Ru(III) was recently accomplished by suitably changing the experimental conditions. It was demonstrated that the primary electron transfer process from Co 3 O 4 to Ru(bpy) 3 3+ in borate buffer solution displays a strong dependence on the buffer concentration and pH . This is attributed to the involvement of a proton‐coupled oxidation of Co(III)‐OH surface sites to Co(IV)=O assisted by a general base catalysis by the B(OH) 4 – base (Figure ) with a kinetic law expressed by Equation and Equation , yielding k B = ca.…”

“…Plot of the electron transfer rate ( k obs ) from Co 3 O 4 nanoparticles to Ru(bpy) 3 3+ vs. base concentration measured at different pH and borate buffer concentrations (base stands for B(OH) 4 – and the concentrations are given by [Base] = f B × [buffer], where f B is the fraction of the basic form of the buffer in solution, estimated considering a p K a = 8.6 for the H 3 BO 3 /B(OH) 4 – couple, and [buffer] is the total buffer concentration). Adapted from ref . with permission from The Royal Society of Chemistry.…”

“…Adapted from ref. [92] plished by suitably changing the experimental conditions. It was demonstrated that the primary electron transfer process from Co 3 O 4 to Ru(bpy) 3 3+ in borate buffer solution displays a strong dependence on the buffer concentration and pH.…”

“…It was demonstrated that the primary electron transfer process from Co 3 O 4 to Ru(bpy) 3 3+ in borate buffer solution displays a strong dependence on the buffer concentration and pH. [92] This is attributed to the involvement of a proton-coupled oxidation of Co(III)-OH surface sites to Co(IV)=O assisted by a general base catalysis by the B(OH) 4 base ( Figure 5) with a kinetic law expressed by Equation (20) and Equation (21), yielding k B = ca. 7×10 2 M -1 s -1 , k OH = 5.5×10 5 M -1 s -1 , and k H2O = 1.7 s -1 .…”