Min Luo,Xin Wang,Taotao Meng,Pei Yang,Ziqi Zhu,Huihua Min,Minzhi Chen,Weimin Chen,Xiaoyan Zhou
Herein, chitosan-based hydrogel beads (CHBs) were used to prepare N- and O-enriched hierarchical porous carbon (PC) by microwave heating for only 10 min. Water molecules in CHBs can act as heating carriers, and the resulting steam not only squeeze out air to create an oxygen-free atmosphere but act as physical activating agent to generate pores. Furthermore, the increased temperature contributed to form chitosan-based char, which, in turn, facilitated microwave absorption to further increase temperature. Considering that KOH as gelling agent of CHBs can also generate pores, the effect of KOH concentration on physicochemical properties of PCs was investigated in detail. Significantly, appropriately higher KOH concentration (3–7%) would cause fiercer reactions to achieve more developed porous structure, while excessive KOH concentration (10%) led to over-etching phenomenon and limited the further development on porous structure. The obtained PCs exhibited large specific surface area up to 1743 m 2 g −1 and O, N-enriched structure (O: 25.1%, N: 4.9%). Particularly, the optimized PC-based electrode prepared by using 7% KOH solution showed remarkably high rate capability (89%). This work provides a one-step and cost-effective method to prepare a promising electrode material for high-rate supercapacitors.
Inhibiting the chlorine evolution reaction (CER) is of great significance for the design and development of oxygen evolution catalysts with high current density for seawater electrolysis. The KOH concentration plays a very important role in controlling the potential of chlorine evolution in seawater electrolysis. However, the effect of its concentration, especially the high one (for example, >1 M), on the OER activity of different catalysts has not been studied so far. Here, we found that the KOH concentration has different linear effects on the OER activity for different catalysts, and we first propose a novel concept named concentration activity coefficient (CAC) to express the linear relationship between the OER activity of the catalyst and the KOH concentration in seawater electrolysis. Based on CAC, we report a Co S-NiFe 2 O 4 catalyst with ultrahigh oxygen evolution activity in the 3 M KOH + seawater. This is due to the strong electronic interaction between Co and S-NiFe 2 O 4 . At current densities of 500 mA cm −2 and 1000 mA cm −2 , the overpotentials of Co S-NiFe 2 O 4 are 270 mV, and 287 mV, respectively, which are much lower than those of the existing electrocatalysts . More promising, the new catalysts also showed a splendid Tafel slope of 18.8 mV dec −1 and a long catalytic lifetime in concentrated alkaline electrolyte . Our findings provide a better understanding of the correlation between the KOH concentration and the OER activity and open new avenues for design and development of electrocatalysts for the next generation of high OER activity in seawater electrolysis.
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