Abstract
Electrochemical CO2 reduction reaction (CO2RR) to fuels and chemicals represents nowadays one of the most challenging solutions for renewable energy storage and utilization. Among the possible reaction pathways, CO2-to-CO conversion is the first (2e−) reduction step towards the production of a key-feedstock that holds great relevance for chemical industry. In this report we describe the electrocatalytic CO2-to-CO reduction by a series of tailored N-decorated carbon nanotubes to be employed as chemoselective metal-free electrocatalysts. The choice of an exohedral functionalization tool for the introduction of defined N-groups at the outer surface of carbon nanomaterials warrants a unique control on N-configuration and electronic charge density distribution at the dangling heterocycles. A comparative electrochemical screening of variably N-substituted carbon nanomaterials in CO2RR together with an analysis of the electronic charge density distribution at each heterocycle have suggested the existence of a coherent descriptor for the catalyst’s CO faradaic efficiency (FECO). Evidence allows to infer that N-configuration (N-pyridinic vs. N-pyrrolic) of exohedral dopants and electronic charge density distribution at the N-neighboring carbon atoms of each heterocycle are directly engaged in the activation and stabilization of CO2 and its reduction intermediates.
Highlights
The steady state increase of CO2 concentration in the atmosphere caused by all main anthropic activities, is largely responsible of global warming effects and associated environmental issues such as climate changes, sea level rise and ocean acidification; phenomena that are seriously affecting our lifestyle
N-content and N-configuration of dangling heterocycles available at the outer material surface (XPS) before being fabricated into carbon cloth (Cc) electrodes and tested as metal-free systems for CO2 reduction reaction (CO2 RR) under comparable conditions
Sample MW@N6 containing carbazole units was prepared as a model of a non-basic N-containing heterocycle embedded in a conjugated sp2 framework similar to MW@N2
Summary
The steady state increase of CO2 concentration in the atmosphere caused by all main anthropic activities (including the massive employ of fossil fuels), is largely responsible of global warming effects and associated environmental issues such as climate changes, sea level rise and ocean acidification; phenomena that are seriously affecting our lifestyle. The development of new (electro)chemical technologies for CO2 conversion into products or energy-vectors of added value represents an effective “two-birds one-stone” approach for mitigating climate effects and supplying the growing energy demand to our modern society [1,2]. CO2 reduction reaction (CO2 RR) into chemicals to be stored, transported and used on demand [3,4]. Energies 2020, 13, 2703 possibility to control the reduction products (i.e., CO, formic acid, alcohols, acetic acid and small hydrocarbons) through the judicious tuning of the potentials applied to the electrochemical cell. Despite the high energetic and environmental significance of CO2 electroreduction, the chemical inertness of CO2 generally requires high applied overpotentials to proceed with its electrochemical conversion
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