Development of Stable CO2 Electro-Reduction Catalyst in Real Water Matrix

Abstract

Artificial photosynthesis refers to the conversion of water and CO2 into value-added chemicals powered by sunlight, and is the holy grail of a sustainable carbon cycle of chemicals. Since a big challenge facing this system is the conversion of stable CO2 into the desired chemicals, most studies have focused on the development of high-performing catalysts within well-refined and restricted test environments. However, such superior performances cannot guarantee their feasibilities in realistic conditions for future commercialization or practical application unless their durability issues are secured. Here we report a one-step ahead approach to develop a more practical and advanced CO2 electro-reduction catalyst with essential clues to overcome the obstacles from realistic conditions, based on the understanding of CO2 reduction reaction deactivation phenomena. Our investigation firstly deals with the performance profile of an Ag electrode, selected as a standard catalyst for CO production, in real-life used tap water which is representative general purpose water. Screening and accompanying thorough analyses on various components in tap water ranging from alkali earth metals to transition/post-transition metals elucidated the types of impurities that can impede the catalytic activity by surface deposition, and consequentially cause the deactivation. Based on the findings involving Ag, a design strategy for a catalyst having excellent tolerance to the deactivation factors was suggested using a carbon-based material with heteroatom-doped active sites. A metal-free nitrogen-doped short carbon nanotube was prepared by a simple three-step process, and was denoted as ball mill N-CNT. As expected, the ball mill N-CNT showed a competitive and tolerant performance to the metal impurities regardless of the nature of the water sources, deionized water and tap water.