Efficient Catalytic Electrode for CO₂ Reduction Realized by Physisorbing Ni(cyclam) Molecules with Hydrophobicity Based on Hansen’s Theory

Abstract

An electrochemical electrode physisorbed with Ni(cyclam) complex molecules containing tetraphenylborate ions (BPh4(-)) as counteranions shows catalytic activity for the reduction reaction of CO2 to CO in an aqueous electrolyte, superior to that of an electrode physisorbed with conventional [Ni(cyclam)]Cl2 complex molecules. The BPh4(-)-containing Ni(cyclam) is inferred as having high hydrophobicity based on its Hansen solubility parameter (HSP), with an interaction sphere excluding HSPs of water in a three-dimensional vector space. The high hydrophobicity of BPh4(-)-containing Ni(cyclam) molecules inhibits their dissolution into aqueous electrolyte and retains their immobilization onto the electrode surface, which we believe to result in the improved catalytic activity of the electrode physisorbed with them. HSP analysis also provides an optimized mixing ratio of solvents dissolving BPh4(-)-containing Ni(cyclam) molecules.

Electrochemical Reduction of Carbon Dioxide to Methanol in the Presence of Benzannulated Dihydropyridine Additives

“…These experimental findings will hopefully motivate better understanding of the mechanism of multi-H + /eprocesses occurring in CO2 electrochemical reduction in the presence of simple organic additives, and lead to the improvements in turnover numbers, for example, by targeting biomimetic hydride shuttles capable of cooperative interactions with electrode surfaces and electric potentials. 24,[49][50][51]…”

Microenvironment Engineering for the Electrocatalytic CO2 Reduction Reaction

“… The hydrophobicity of eCO 2 RR electrodes achieved via other pathways: a) constructing hierarchical architectures, [23] and b) modifying with metal complexes [33] . Adapted, with permission, from: Ref.…”

“…[23], Copyright 2021 American Chemical Society, and Ref. [33], Copyright 2016 American Chemical Society.…”

Liquid-Repellent Films Comprising Octamethylsilsesquioxane Selected Based on Three-Dimensional Solubility Parameters

“…We have previously evaluated hydrophobicity of a catalytic molecule for enhancing CO 2 reduction reaction in this way. 24 HSP of various substances have been reported, collected, 25 and stored in a database for use with commercial software (HSP in Practice 5th ed., ver. 5.0.08).…”

“…For instance, two substances with HSP located close to each other have similar solubility, whereas the farther the distance between the HSP of two substances, the larger the difference in solubility. We have previously evaluated hydrophobicity of a catalytic molecule for enhancing CO 2 reduction reaction in this way …”