Copper-based Reducible Composite Electrocatalysts for Carbon Dioxide Reduction

• Main Author: Amaha Woldu Kahsay
• Other Authors: Bing-Joe Hwang
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/suxj4r

博士 === 國立臺灣科技大學 === 化學工程系 === 107 === Conversion of earth-abundant CO2 into value-added chemicals is an important means to reduce its accumulation in the atmosphere and compact global warming and climate change related to environmental threats. Among different approaches to convert CO2 into useful reduction products, electrochemical CO2 reduction is the most promising and sustainable method to mitigate CO2 emission. One of the most critical challenges in electrochemical CO2 reduction is to overcome the activation energy and increase the sluggish kinetics of electrochemical conversion, which will demand the developments of active and selective electrocatalysts. So far copper based electrocatalysts are most appropriate candidates for CO2 conversion to hydrocarbons and alcohols. Tremendous research efforts exerted and remarkable progress has been made so far. However, poor selectivity, activity, durability and high overpotential requirement still limits their practical applications. The objectives of this dissertation work are to overcome those bottleneck challenges by developing new electrocatalyst using simple and scalable methods. In our first work, we have investigated the effect of highly concentrated bicarbonate electrolyte on the electrochemical performance of CO2 reduction on copper mesh electrode. High concentrated electrolytes have shown significantly increased total reduction activities as concentration increased. The specific product analysis using gas chromatography indicates hydrogen generation is the highly dominant and electrochemical conversion of CO2 into gaseous products on copper mesh in high concentrated KHCO3 (2 M, 3 M, and 4 M) at the specified potential was not observed. This could be attributed to the insolubility of carbon dioxide in concentrated aqueous solution. In our second work, we have synthesized Cu-Pb based oxides (CuPbyOx-5/CP) using electrochemical deposition method. The synthesized electrocatalyst has demonstrated better electrochemical CO2 reduction activity compared with pristine oxides prepared with a similar method. The LSV result demonstrates significantly improved total current density and selectivity of the optimized composites catalyst for CO2 conversion. The incorporation of lead oxides could be favoring selective CO2 conversion over hydrogen evolution reaction. In our third work, for the first time, perovskite derived lead composite decorated copper nanowires (CuNWs@pervo) has been synthesizing as new electrocatalyst for electrochemical CO2 reduction. The electrocatalyst prepared at 200 °C for 1 hr (CuNWs@pervo) offered remarkably enhanced CO2 reduction activities by suppressing the hydrogen evolution reaction. FE of 43% and 59% of H2 and HCOO¬- with a total current density of -15.5 mAcm-2 at -1.0 V vs.RHE were obtained at lead composite modified copper nanowire prepared from ammonium lead iodide. In the final work, we fabricated environment-friendly and earth-abundant, copper sulfide decorated copper heterostructure(Cu2O/CuO/CuS-20) electrocatalyst using facile and simple SILAR method. The main idea here is to maintain copper oxide by decorating with copper sulfide. The modified electrocatalyst exhibited high selectivity for formate formation at low overpotential. Remarkably, maximum faradaic efficiency of 84% and enhanced partial current density of -20 mA cm-2 were obtained at applied potential of -0.7 V