Functional and innovative carbon nitride/hydroxyapatite composite material for efficient carbon dioxide electrocatalytic reduction to formic acid

CO2 conversion is one of the most encouraging approaches among carbon capture and utilization technologies (CCUs) to recycle carbon dioxide emissions on a large scale. Among CCUs, CO2 electrochemical reduction (CO2-ER) represents a promising strategy in CO2 emission recycling. However, CO2-ER faces various challenges, such as energy efficiency, reaction selectivity, and conversion rate that can be overcome with the proper design of an electrocatalyst1. Here, we present an innovative composite material(Fig.1) composed of graphitic carbon nitride (CN), obtained by pyrolysis of a covalent organic framework as a precursor2, decorated by copper nanoparticles(Cu) and hydroxyapatite nanorods. The latter is introduced as a key-component to decrease overpotential and increase efficiency towards the production of value-added molecules, such as formic acid3. Morphological, spectroscopic and thermal analyses were conducted on the obtained material HAP_Cu@CN. The performance of HAP_Cu@CN in CO2-ER were evaluated and compared with those of other copper-carbon based catalysts. Electrochemical investigations were carried out using a three-electrode cell in a 0.1 M KHCO3 aqueous solution(Fig.2,a). Linear sweep voltammetry curves showed that admixing with HAP resulted in a slight increase in system activity. The chronoamperometric tests revealed that the HAP-based catalyst showed higher CO2-ER activity than the other catalysts. Specifically, at -1.8 V applied potential (vs Ag-AgCl), parasitic H2 faradic efficiency (FE) decreased by 40% and HCOOH became the main product with a 50% FE, while other Cu-based materials were more efficient for hydrogen production without a positive effect on product distribution and selectivity(Fig.2,b). The composite material showed promising results in CO2ER, demonstrating that combining different surfaces can pave the way for more efficient and selective electrocatalysts.