Zhang Yonghui, Xu Xin, Geng Qingxuan, Li Qingwei, Li Xiuli, Wang Yixuan, Tang Zihuan, Gao Biao, Zhang Xuming, Chu Paul K, Huo Kaifu
The State Key Laboratory of Refractories and Metallurgy, Institute of Advanced Materials and Nanotechnology, Wuhan University of Science and Technology Wuhan 430081 China.
Wuhan National Laboratory for Optoelectronics (WNLO), School of Optical and Electronic Information, Huazhong University of Science and Technology Wuhan 430074 China
Chem Sci. 2024 Dec 13;16(4):2034-2043. doi: 10.1039/d4sc07145j. eCollection 2025 Jan 22.
Alkali activation is a common method to prepare commercial porous carbon. In a mixed alkali activation system, the role of each individual alkali has generally been assumed to be the same as in a single alkali activation system, and the low corrosiveness of weak alkalis has mainly been emphasized. However, the intrinsic roles of the individual alkalis should be understood in detail and redefined to illuminate the activation pathways from the perspective of internal chemical reactions rather than corrosiveness. Herein, by combining TG-MS analysis, DFT calculation and other characterizations, the activation processes were precisely tracked, and activation pathways were proposed. In the mixed alkali activation system, the strong alkali KOH served as the activation promoter, first decomposing into KO, which then attacked the C-C bonds to form active reaction sites defined as pore seeds. The weak alkali KCO acted as the activation pathway modifier; CO preferentially etched the pore seeds over KO due to the lower reaction barrier of CO interacting with the pore seeds. Consequently, the rough etching reaction of KOH was replaced and suppressed by the gentler action of CO , forming more micropores. When the ratio of strong to weak alkali was 1 : 1, the obtained CKK-122 exhibited the highest microporosity (82.61%) and a high specific surface area (1962.18 m g). It exhibited a high specific capacitance of 296.7 F g and excellent cycling stability with 98.3% retention after 10 000 cycles. The supercapacitor demonstrated a high energy density of 114.4 W h kg at a power density of 17.5 kW kg, with a broad potential window of 3.5 V.
碱活化是制备商业多孔碳的常用方法。在混合碱活化体系中，通常认为每种碱的作用与单一碱活化体系相同，并且主要强调了弱碱的低腐蚀性。然而，应详细理解并重新定义每种碱的内在作用，以便从内部化学反应而非腐蚀性的角度阐明活化途径。在此，通过结合热重-质谱分析、密度泛函理论计算和其他表征手段，精确追踪了活化过程，并提出了活化途径。在混合碱活化体系中，强碱KOH作为活化促进剂，首先分解为KO，然后KO攻击C-C键形成定义为孔核的活性反应位点。弱碱K₂CO₃作为活化途径调节剂；由于CO₂与孔核相互作用的反应势垒较低，CO₂优先蚀刻孔核而非KO。因此，KOH的粗糙蚀刻反应被CO₂的温和作用取代并抑制，形成了更多的微孔。当强碱与弱碱的比例为1:1时，所得的CKK-122表现出最高的微孔率（82.61%）和高比表面积（1962.18 m²/g）。它表现出296.7 F/g的高比电容和优异的循环稳定性，10000次循环后保留率为98.3%。该超级电容器在功率密度为17.5 kW/kg时表现出114.4 W h/kg的高能量密度，具有3.5 V的宽电位窗口。
