Efficient Electrochemical CO2 Reduction via Nickel−Nitrogen Sites Hollow Carbon Spheres

After 19^th century, carbon dioxide (CO₂) and other green house gases has increased more amount of heat which have “trapped” in the earth's atmosphere and automatically global temperature rises. It causes significant climatic changes as well as the amount and frequency of precipitation. It can also increases in extreme weather conditions such as flooding, droughts, hurricanes, and wildfires. It also effects in ecosystem changes, rising sea levels, and food insecurity.

Carbon dioxide can be emitted from energy process raw materials, run computers, that have been used at factories and other facilities to run machines, heat and cool buildings, which are connected to the internet, etc.

CO₂ emissions can also be directly caused by leakage in the use of petroleum production, other industrial process and chemical reactions during the manufacturing process. Indirect emissions are observed from the energy production off-site, such as the emissions created by the power plants which facilities to get the electricity.

Scientists need to be focused on the reduction of CO₂ (excess) present in our atmosphere. In this field, it is more important because of reducing CO₂ into high value-added products as well as useful chemicals and the critical issues of CO₂ emission from fossil fuels. The electrochemical reduction of CO₂ (ERC) reaction is one of the effective finding on this field, but it can’t realize the conversion of carbon dioxide, however, it can also store intermittent renewable electricity by driving the ERC.

Currently many researches are going on “CO₂ reduction” but reducing CO₂ to high value-added chemicals is of high significance due to its vital role in mitigating CO₂ emission and energy crisis. Therefore new finding on robust catalysts with low overpotential, stability is extremely challenging of high selectivity.

The ERC reaction mainly needs an effective catalyst; in this case many types of catalysts are reported such as metals, metal oxides, metal alloys and metal chalcogenides. However, these catalysts are very expensive and inferior to activity and selectivity, accordingly within their limits of practical large-scale application. Therefore, carbon-based catalysts have intrigued enormous interest due to their high stability, conductivity, low cost and tunable porous structure.

Now-a-days, the transition metal (M = Ni, Fe, Co etc.) of single atom anchored on N-doped carbons (M−N−C) has demonstrated unexpected activity and selectivity for ERC reaction compared to other carbon based catalysts.

Prof. Xianfeng Li and his team have reported on a single Ni atom anchored with N-doped carbon (Ni−N−C) catalyst, which was designed and prepared via facile synthesis method to embed highly and evenly dispersed, coordinated unsaturated nickel−nitrogen active sites into a hollow carbon matrix with abundant micropores [1].

This reported catalyst possesses a unique electronic structure, maximized atomic utilization, and coordination environment. Also, this catalyst shows a higher intrinsic activity and remarkable selectivity for the ERC reaction. Further, the content of Ni and coordination structure can be easily modulated by changing the calcination temperature. It has also plays a vital role for the catalytical performance. From this research report, the Ni−N−C catalysts can be achieved over 90% for CO at a wide potential window from −0.6 to −1.0 V with a maximum value of 97% at −0.8 V. They have designed a facile way to develop high-performance single atomic catalysts with a tunable Ni−N coordination structure for CO₂ reduction.

Figure 1. Images of the Ni/N-doped hollow carbon spheres (HCSs) and Faradaic efficiencies (FEs) of CO at various applied potentials for Ni/N-HCS-T and N-HCS-1000 [1].

The porous carbon spheres have analogous behavior due to controlled porous structures, surface functionality, large surface area and high electrical conductivity. The main research finding of this work is that the high-density unsaturated Ni−N active sites can efficiently adsorb and activate CO₂, which can improve particularly the selectivity toward ERC products. In this case, maximum 97% of CO was obtained from ERC reaction.

The Ni-N-C catalyst possesses a high content of low-coordinated unsaturated Ni−N sites, electronic conductivity, and fast kinetics, which are beneficial to improve the electrocatalytic selectivity and activity and stability of the catalyst also plays a vital role for the CO₂ reduction reaction.

Our SNB team have mainly emphasize this new research article to enrich our viewer’s knowledge about the area of intense research on Efficient electro chemical CO₂ reduction via nickel−nitrogen sites hollow carbon spheres. Furthermore, their main research findings explains the following aspects viz., (i) A facile synthesis method embeds single-dispersed coordinatively unsaturated Ni−N active sites in a hollow carbon matrix with abundant micropores for the highly efficient CO₂ reduction reaction. (ii) Single Ni atom is attributed to the high N content of melamine. (iii) It can anchor Ni atoms to form the Ni−N active sites at a high temperature, and the abundant micropores of hollow carbon sphere and can absorb and confine hydrated Ni²⁺ into its micropores during the calcinating process, further preventing the aggregation of Ni atoms. (iv) Calcination temperature plays a vital role to change the coordination structure and content of Ni which can be easily modified on carbon hollow sphere. (v) From ERC reaction, the results can be achieved over 90% FE for CO at the wide potential window from −0.6 to −1.0 V and maximum CO obtained about 97% at −0.8 V, these catalyst have high content of the low-coordinated unsaturated Ni−N sites, high electronic conductivity, and fast kinetics. (vi) The ERC reaction is mainly to form CO₂^•− intermediate with fast electron transfer kinetics which can reduce the overpotential. (vii) The low coordinated unsaturated Ni−N sites can reduce the free energy of *COOH and also to promote the desorption step of *CO, which are beneficial to improve the electrocatalytic performance for ERC products. (viii) It also shows good durability of continuous reaction for 11 h.

Hence, these results paves a facile way to develop a nonprecious metal single-atom catalyst with a tunable coordinated environment and Ni loading for the electrocatalytic fields.

Reference

1. P. Yao et al., ACS Sustainable Chem. Eng. 9 (2021) 5437−5444.

--- Dr. A. S. Ganeshraja

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