Enhanced Kinetics of Hole Transfer and Electrocatalysis during Photocatalytic Oxygen Evolution by Cocatalyst Tuning

Abstract

Understanding photophysical and electrocatalytic processes during photocatalysis in a powder suspension system is crucial for developing efficient solar energy conversion systems. We report a substantial enhancement by a factor of 3 in photocatalytic efficiency for the oxygen evolution reaction (OER) by adding trace amounts (~0.05 wt%) of noble metals (Rh or Ru) to a 2 wt% cobalt oxide-modified Ta3N5 photocatalyst particulate. The optimized system exhibited high quantum efficiencies (QEs) of up to 28 and 8.4% at 500 and 600 nm in 0.1 M Na2S2O8 at pH 14. By isolating the electrochemical components to generate doped cobalt oxide electrodes, the electrocatalytic activity of cobalt oxide when doped with Ru or Rh was improved compared with cobalt oxide, as evidenced by the onset shift for electrochemical OER. Density functional theory (DFT) calculation shows that the effects of a second metal addition perturbs the electronic structure and redox properties in such a way that both hole transfer kinetics and electrocatalytic rates improve. Time resolved terahertz spectroscopy (TRTS) measurement provides evidence of long-lived electron populations (>1 ns; with mobilities μe ~0.1-3 cm 2 V -1 s -1 ), which are not perturbed by the addition of CoOx-related phases. Furthermore, we find that Ta3N5 phases alone suffer ultrafast hole trapping (within 10 ps); the CoOx and M-CoOx decorations most likely induce a kinetic competition between hole transfer toward the CoOx-related phases and trapping in the Ta3N5 phase, which is consistent with the improved OER rates. The present work not only provides a novel way to improve electrocatalytic and photocatalytic performance but also gives additional tools and insight to understand the characteristics of photocatalysts that can be used in a suspension system.

Towards Versatile and Sustainable Hydrogen Production through Electrocatalytic Water Splitting: Electrolyte Engineering

“…One successful example of this is the addition of an oble metal to the transition metal oxide. [142][143][144][145][146][147][148] Improving not only the activity but also the stabilityisachallenge for OER electrodes, particularly in acidic [149] and nearneutralp H [150] environments. At rade-off between the activity and stability is reported for the OER in acidic environments, even for the most active oxides, IrO 2 and RuO 2 .…”

Boosting the Performance of the Nickel Anode in the Oxygen Evolution Reaction by Simple Electrochemical Activation

“…Ir‐ or Ru‐based oxide electrodes have been recognized for their outstanding OER performance; however, the scarcity and high cost of such noble metals hamper their widespread usage. Accordingly, electrocatalysts made of earth‐abundant elements have been the subject of extensive research activity in recent decades . Particularly, NiFe (hydr)oxide has attracted tremendous attention, owing to its superior performance at alkaline pH; a current density of 10 mA cm −2 was attained at ca.…”

Boosting the Performance of the Nickel Anode in the Oxygen Evolution Reaction by Simple Electrochemical Activation

“…[7] Ir-orRu-based oxide electrodes have been recognized for their outstanding OER performance; [8][9][10] however, the scarcity and high cost of such noble metals hamper their widespread usage.A ccordingly,electrocatalysts made of earth-abundant elements have been the subject of extensive research activity in recent decades. [4,[11][12][13][14] Particularly,N iFe( hydr)oxide has attracted tremendous attention, [4,11,12,15,16] owing to its superior performance at alkaline pH;acurrent density of 10 mA cm À2 was attained at ca. 1.5 V RHE under ambient conditions.…”