Evidence for Distinct Active Sites on Oxide-Derived Cu for Electrochemical Nitrate Reduction
Jiguang Zhang, Linrong Huang, Weng Weei Tjiu, Chao Wu, Mingsheng Zhang, Surani Bin Dolmanan, Sibo Wang, Meng Wang, Shibo Xi, Zainul Aabdin, Yanwei Lum
Abstract
Cu is a promising catalyst for electrochemical nitrate (NO 3 – ) reduction. However, desorption of the nitrite (NO 2 – ) intermediate can occur, leading to lowered ammonia productivity and Faradaic efficiency. Here, we discovered that this does not occur with oxide-derived Cu due to the presence of at least two distinct types of cooperative active sites: one for NO 3 – → NO 2 – and another for NO 2 – → NH 3 . As a result, oxide-derived Cu exhibits enhanced ammonia productivity with a mixed NO 3 – /NO 2 – feed relative to pure NO 3 – or NO 2 – . In contrast, this was not observed with a standard Cu sample, implying the presence of only a single type of active site. Our dual-site hypothesis was supported by attenuated total reflection surface enhanced infrared absorption spectroscopy and isotopic labeling experiments involving co-reduction of 15 NO 3 – / 14 NO 2 – . We also successfully simulated our experimental results using a mathematical model involving two different adsorption sites. These findings motivate the need for further study and rational design of such active sites.