Systematic Influence of Electronic Modification of Ligands on the Catalytic Rate of Water Oxidation by a Single‐Site Ru‐Based Catalyst

Abstract

Catalytic water oxidation is an important process for the development of clean energy solutions and energy storage. Despite the significant number of reports on active catalysts, systematic control of the catalytic activity remains elusive. In this study, descriptors are explored that can be correlated with catalytic activity. [Ru(tpy)(pic) 2 (H 2 O)](NO 3 ) 2 and [Ru(EtOtpy)(pic) 2 (H 2 O)](NO 3 ) 2 (where tpy = 2,2' : 6',2"-terpyridine, EtOtpy = 4'-(ethoxy)-2,2':6',2"-terpyridine, pic = 4-picoline) are synthesized and characterized by NMR, UV/Vis, EPR, resonance Raman, and X-ray absorption spectroscopy, and electrochemical analysis. Addition of the ethoxy group increases the catalytic activity in chemically driven and photocatalytic water oxidation. Thus, the effect of the electron-donating group known for the [Ru(tpy)(bpy)(H 2 O)] 2 + family is transferable to architectures with a tpy ligand trans to the Ru-oxo unit. Under catalytic conditions, [Ru(EtO-tpy)(pic) 2 (H 2 O)](NO 3 ) 2 displays new spectroscopic signals tentatively assigned to a peroxo intermediate. Reaction pathways were analyzed by using DFT calculations. [Ru(EtOtpy)(pic) 2 (H 2 O)](NO 3 ) 2 is found to be one of the most active catalysts functioning by a water nucleophilic attack mechanism.

Evaluation of Ce-MOFs as Photoanode Materials for the Water Oxidation Reaction: The Effect of Doping with [Ru(bpy)(dcbpy)(H2O)2]2+ Catalyst

“…Specifically, water splitting represents the most promising pathway for advancing the development of clean and renewable energy. 1,2 The main challenge in hydrogen production through water splitting is the complex multielectron water oxidation reaction (WOR). To efficiently convert sunlight into chemical energy, we need photocatalytic materials that can absorb visible light photons, generate charge-separated states with suitable redox potentials, have high activity for water splitting and are high durable in the harsh chemical conditions of WOR.…”

“…To meet this demand, we have primarily relied on fossil fuels; however, the consumption of fossil fuels increases greenhouse gas emissions, notably carbon dioxide (CO 2 ), introducing the foreboding presence of global warming and climate change. Therefore, there is an urgent need for green and clean energy sources as replacements for fossil fuels. − Harnessing sunlight through artificial photosynthesis has emerged as a highly effective approach for producing carbon-free and environmentally friendly fuel. Specifically, water splitting represents the most promising pathway for advancing the development of clean and renewable energy. , The main challenge in hydrogen production through water splitting is the complex multielectron water oxidation reaction (WOR).…”

“…Therefore, there is an urgent need for green and clean energy sources as replacements for fossil fuels. − Harnessing sunlight through artificial photosynthesis has emerged as a highly effective approach for producing carbon-free and environmentally friendly fuel. Specifically, water splitting represents the most promising pathway for advancing the development of clean and renewable energy. , The main challenge in hydrogen production through water splitting is the complex multielectron water oxidation reaction (WOR). To efficiently convert sunlight into chemical energy, we need photocatalytic materials that can absorb visible light photons, generate charge-separated states with suitable redox potentials, have high activity for water splitting and are high durable in the harsh chemical conditions of WOR.…”

Computational Analysis of Structure–Activity Relationships in Highly Active Homogeneous Ruthenium−Based Water Oxidation Catalysts

“…For most Ru-based catalysts, O-O bond formation from Ru IV intermediates via WNA or I2M processes is difficult; access to the high-valent Ru V =O intermediate lowers barriers sufficiently to allow for O-O bond formation. However, in many Ru-based WOCs, direct oxidation from Ru IV =O to Ru V =O occurs at high potentials (≥1.7V) [ 41 , 43 , 44 ]. At the same time some Ru-based WOCs boast very high rates of oxygen evolution.…”

“…In the case of WNA, a Ru−oxo species is attacked by a solvent water molecule with a proton transfer, succeeded by further electron transfer prior to, or in concert with, the release of molecular oxygen (details of these later steps were not investigated); I2M mechanisms simply involve a coupling of two metal−oxo groups, resulting in the O−O bond requisite for O 2 evolution. A substantial history of work on Ru−based WOCs [39,[41][42][43][44] suggests that both WNA and I2M processes occur more easily upon reaching the high−valent Ru V = O state. Such studies describe the catalytic cycles leading to O 2 evolution in roughly four steps, each characterized by the removal of one electron:…”