A highly active nickel electrocatalyst shows excellent selectivity for CO₂ reduction in acidic media

Abstract

The development of selective electrocatalysts for CO₂ reduction in water offers a sustainable route to carbon based fuels and feedstocks. However, molecular catalysts are typically studied in non-aqueous solvents, in part to avoid competitive H₂ evolution. [Ni(cyclam)]²⁺ (<b>1</b>) is one of the few known electrocatalysts that operate in water and 30 years after its report its activity remains a rarely surpassed benchmark. Here we report that [Ni(cyclam-CO₂H)]²⁺ (cyclam-CO₂H = 1,4,8,11-tetraazacyclotetradecane-6-carboxylic acid (<b>2</b>)) shows greatly enhanced activity <i>versus</i><b>1</b> for CO production. At pHs < p<i>K</i>_a of the pendant carboxylic acid a large increase in catalytic activity occurs. Remarkably, despite the high proton concentration (pH 2), <b>2</b> maintains selectivity for CO₂ reduction and is believed to be unique in operating selectively in such acidic aqueous solutions.