Synergistic Conversion Of Coal Char And Methane For Co-Production Of Carbon Materials And Hydrogen/Syngas

Supercapacitors,between traditional batteries and capacitors,have good performance in energy storage/release and application environment,and have been used in combination with other energy storage devices in various fields.Electrodes are extremely important components of supercapacitors,which determine the electrochemical performance of supercapacitors.Among them,carbon materials have been widely studied due to their large specific surface area,tunable pore size and stable energy storage,but their defects of low energy density have not been effectively improved.Pseudocapacitive materials are another important electrode materials,which can store huge energy through redox reactions.However,the disadvantages of poor electrical conductivity and poor stability of pseudocapacitive materials affect their industrial application.Combining the advantages of the two to design and prepare electrode materials with better performance provides a new way to solve the current problems.In this paper,coal char was selected as raw material,by adding metal components or introducing chemical activator K₂CO₃,to use for catalytic methane decomposition（CMD）or dry methane reforming reaction（DMR）to realize the co-production of functional composite materials and hydrogen/syngas.The main findings are as follows:（1）coal char,with introduction of Ni or Fe,was used for CMD after steam gasification.During steam gasification,a fuel gas rich in H₂（>60%）（consisting of H₂,CO₂,CO,and CH₄）could be generated through the cycle of steam gasification of coal char and oxidation-reduction of metals.The pore structure of the solid residue after partial gasification reaction was effectively improved.For example,the specific surface area and pore volume of the gasification residue sample CC-7Ni3Fe reached 240 m²/g and 0.141 cm³/g,respectively（coal char was 6 m²/g and 0.009 cm³/g,respectively）.In CMD,the reaction activity of the Ni-Fe bimetallic catalyst sample was better than single metal catalyst,and the conversion rate of methane was still stable at about 75%after 600 min.However,the electrochemical performance of the solid products of the CMD was poor,even worse than coal char after steam gasification.（2）In order to improve the electrochemical performance of the above-mentioned complexes of coal char-based carbon and carbon deposits of CMD,K₂CO₃ and CO₂ were introduced to constitute a synergistic conversion process of CC and methane under the action of K₂CO₃ catalysis.the electrochemical properties of the carbon-iron composites obtained after the reaction were used as indicators to investigate the effects of the Fe ratio,CC/K₂CO₃ratio,CH₄/CO₂ flow ratio and reaction time.It was found that when the reaction temperature was 850°C,the mass ratio of CC to Fe was 4:0.05 g,the mass ratio of CC to K₂CO₃ was 4:4g,the flow ratio of CH₄/CO₂ was 30/50,and the reaction time was 180 min,The specific surface area of CC15 sample is 219 m²/g,the pore volume is 0.135 cm³/g,the microporosity is 56%,thus the electrochemical performance of which was excellent.At 1 A/g,the capacitance value of CC15 electrode material reached 316.8 F/g,which was 270%higher than that of CC electrode（85.4 F/g）.After 5000 continuous charge/discharge tests at 10 A/g,it was found that the capacitance retention rate was 68.9%.Under the corresponding conditions,the conversion rates of CH₄ and CO₂ in the CC15 sample reached 70%and 93%,respectively（CC was 31%and 84%）,indicating that introducing of K₂CO₃ and CO₂ played an important role in reducing carbon emissions.The activation of the matrix,improved the electrochemical performance of the composite electrode and achieving co-transformation of CC and methane to co-produce carbon materials and syngas.CC15 and commercial activated carbon（specific surface area and pore volume of 940 m²/g and 0.56 cm³/g,respectively）were assembled into asymmetric supercapacitors as positive/negative electrodes,respectively,to evaluate the practical application of CC15 composites.The results indicated that the asymmetric supercapacitor achieved an energy density of 19.5 Wh/kg at a power density of 70.2 W/kg;and an energy of 6.1 Wh/kg at a power density of 21.8 W/kg.At the same time,the capacitor can still maintain 81%of the original capacitance after 2000 cycles at 5 A/g.In this paper,the co-production of functional carbon materials and hydrogen/synthesis gas was achieved through the co-conversion process of CC and methane.it not only realized the high-value utilization of coal char,but also provided theoretical guidance for the cooperative low-carbon conversion of coal char and natural gas.