Electrocatalysts for Water Splitting and Carbon Dioxide Reduction Reaction

With the growth of global population and the advancement of civilization, the energy demand is increasing rapidly. It’s reported that the global annual energy demand is around 12 billion tons of oil equivalent and lead to 39.5 Giga tons of CO2 gas. In 2013, carbon dioxide (CO2) concentration in the atmosphere reached 400 parts per million for the first time in human history. The rise of CO2 level is believed to be one of the major reasons for the anthropogenic climate change, and it’s urgent to find a promising method to reduce the atmospheric CO2 level. Reducing CO2 emission by using alternative clean fuels, e.g., hydrogen fuel, is one of the promising methods. Electrolysis of water is one of most efficient and environmentally friendly methods to generate hydrogen gas and attracted a lot of attention recently. High-efficient, low-cost, and stable catalysts are required for both cathode and anode to reduce the activation energy barriers for hydrogen and oxygen evolution reactions. Significant advances have been made lately in developing water splitting catalysts, but there is still a lot of room for improvement. Directly reduction of CO2 into useful products is another promising method to reduce atmospheric CO2 level. We can achieve a dual benefit by converting atmospheric CO2 into value-added chemicals. Importantly, with the increasing prevalence of wind and solar power, the cost of electricity continues to decrease. Abundant and low-cost renewable electrical energy sources make electrochemical reduction of CO2 an attractive and promising solution for CO2 mitigation. As a result, enormous effort has recently been devoted to exploring novel catalysts for electrochemical CO2 reduction reactions (CO2RR), with a goal of achieving improved selectivity, activity, and stability. This dissertation covers my five years’ study on designing and preparing catalysts for water splitting and electrochemical CO2 reduction. For water splitting, we used a 3D printing technique to develop a new porous electrode with periodic pore structures. These pores aligned in the same direction and act as built-in gas bubble flow channels that effectively suppressed bubble coalescence, jamming, and trapping and, hence, result in rapid bubble release. The 3D printed electrodes decorated with catalysts achieved a high current density of 1000 mA cm−2 at fairly low hydrogen evolution reaction and oxygen evolution reaction overpotentials. For electrochemical CO2 reduction, we developed a new Cu2O/CuS composite catalyst that simultaneously achieves an excellent faradaic efficiency of 67.6% and a large partial current density for generating formate. More importantly, it maintains the catalytic performance for at least 30 hours. The findings provided critical insights in the role of CuS in stabilizing the catalyst under CO2 reduction conditions. My second CO2 reduction project aims to enhance the selectivity and activity for carbon dioxide reduction towards C2+ alcohols (ethanol and propanol). We developed Cu-Ce catalysts for CO2 reduction towards C2+ alcohols. Interfacing Cu and Ce and tuning the Cu/Ce ratio can modify the catalyst’s electronic properties for improving CO adsorption. The Cu-Ce catalyst showed ~35% Faradaic efficiency towards C2+ alcohols, which is almost twice as that of the Cu control sample