Design of experiments unravels insights into selective ethylene or methane production on evaporated Cu catalysts

Abstract

As a highly tempting technology to close the carbon cycle, electrochemical CO2 reduction calls for the development of highly efficient and durable electrocatalysts. In the current study, Design of Experiments utilizing the response surface method is exploited to predict the optimal process variables for preparing high-performance Cu catalysts, unraveling that the selectivity towards methane or ethylene can be simply modulated by varying the evaporation parameters, among which the Cu film thickness is the most pivotal factor to determine the product selectivity. The predicted optimal catalyst with a low Cu thickness affords a high methane Faradaic efficiency of 70.6% at the partial current density of 211.8 mA cm−2, whereas that of a high Cu thickness achieves a high ethylene selectivity of 66.8% at 267.2 mA cm−2 in the flow cell. Further structure-performance correlation and in-situ electro-spectroscopic measurements attribute the high methane selectivity to isolated Cu clusters with low packing density and monotonous lattice structure, and the high ethylene efficiency to coalesced Cu nanoparticles with rich grain boundaries and lattice defects. The high Cu packing density and crystallographic diversity is of essence to promoting C–C coupling by stabilizing *CO and suppressing *H coverage on the catalyst surface. This work highlights the implementation of scientific and mathematic methods to uncover optimal catalysts and mechanistic understandings toward selective electrochemical CO2 reduction.