The Implications of Coupling an Electron Transfer Mediated Oxidation with a Proton Coupled Electron Transfer Reduction in Hybrid Water Electrolysis

Abstract

Electrolysis of water is a sustainable route to produce clean hydrogen. Full water‐splitting requires a high applied potential, in part because of the pH‐dependency of the H2 and O2 evolution reactions (HER and OER), which are proton‐coupled electron transfer (PCET) reactions. Therefore, the minimum required potential will not change at different pHs. TEMPO [(2,2,6,6‐tetramethyl‐1‐piperidin‐1‐yl)oxyl], a stable free‐radical that undergoes fast electro‐oxidation by a single‐electron transfer (ET) process, is pH‐independent. Here, we show that the combination of PCET and ET processes enables hydrogen production from water at low cell potentials below the theoretical value for full water‐splitting by simple pH adjustment. As a case study, we combined the HER with the oxidation of benzylamine by anodically oxidized TEMPO. The pH‐independent electrocatalytic oxidation of TEMPO permits the operation of a hybrid water‐splitting cell that shows promise to perform at a low cell potential (≈1 V) and neutral pH conditions.

Non‐Equilibrium Assembly of Atomically‐Precise Copper Nanoclusters

“…It can be assumed that the Cu(I) oxidation (φ Cu2+/Cu+ : 0.82 V < φ O2 / H2O : 1.23 V) led to the disintegration of CuNCs into cluster fragments, such as Cu n +1 L n + ( n = 3, 4, 5, and 6). [ 19 ] The ligands and Cu(II) ions, with smaller ionic radii, then re‐organized into metastable CuL 2 ( R 2 , Figure a). [ 18,20 ] Furthermore, these non‐equilibrium Cu n +1 L n + assemblies are highly vulnerable and readily undergo complete oxidation into CuL 2 /Cu 2+ (Figure S9, Supporting Information).…”

“…The declined O 2 /H 2 O potential should be responsible for the prolonged t 2 , where the potential difference (Δ E = φ O2/H2O − φ Cu2+/Cu+ , Figure S24 and Table S6, Supporting Information) decreases at basic conditions, leading to a weaken copper oxidation rate. [ 19a ] In addition, pH can also affect t 3 , the acidic environments increase the dissociated Cu 2+ concentration instead of forming insoluble copper hydroxide, [ 34 ] favoring the ligand exchange reaction. O 2 pressure could be used as an alternative method to influence the O 2 /H 2 O potential, according to the Nernst equation (φ O2/H2O = 1.23 + 0.059lg[p O2 ·c H + ]).…”

Proton‐Coupled Electron Transfer in Electrocatalytic Water Splitting

“…Understanding the details of PCET is helpful to design more efficient catalysts to promote the overall efficiency of hydrogen production from water splitting. [9]…”

“…In recent years, PCET has been shown as critical steps in electrocatalytic water splitting. Understanding the details of PCET is helpful to design more efficient catalysts to promote the overall efficiency of hydrogen production from water splitting [9] …”