Bi‐Directional Electrolytic Reduction of CO₂ to Mesoporous Carbons with Regulated Structure and Surface Functional Groups for Zn‐ion Capacitors

Abstract

Zn‐ion capacitors (ZICs) take advantage of batteries and supercapacitors in delivering high energy and power densities for energy storage by using porous carbons due to their low cost, lightweight, high conductivity, and good stability. However, it remains a grand challenge to regulate the mesoporous structures of carbons, including pore sizes and surface functional groups, which are essential for ion transport and electrochemical reactions of ZICs. Herein, a bi‐directional electrolysis strategy is developed to directly reduce CO2 to oxygen‐rich mesoporous carbons (OMCs) with adjustable pore sizes and oxygen‐bearing functional groups, which are preferred for ZICs as theoretically proved by density functional theory (DFT). The designed OMCs exhibit a remarkable energy density of 216.6 Wh kg−1 and performance retention of 90% after 15000 cycles. When assembled in the flexible ZICs, the OMCs demonstrate a high capacitance of 329.5 mAh g−1. This work presents a novel strategy for synthesizing OMCs through a decarbonization process and reveals the crucial role of microstructure and surface functional groups in promoting the performance of ZICs.

Molten Salt Electrolytic CO2-Derived Carbon-Based Nanomaterials for Energy Storage and Electrocatalysis: A Review

“…59,60 This enhancement occurs through the following reactions: C 61,62 Although the oxygen-containing carbons have many advantages for ZICs, only a few works about the CO 2 -C were reported. 15,63 Li and Yang et al reported a CO 2 -derived OMC for ZICs. 15 OMC was innovatively obtained through bidirectional electrolytic reduction of CO 2 in a molten Li 2 CO 3 −Na 2 CO 3 −K 2 CO 3 .…”

“…15,63 Li and Yang et al reported a CO 2 -derived OMC for ZICs. 15 OMC was innovatively obtained through bidirectional electrolytic reduction of CO 2 in a molten Li 2 CO 3 −Na 2 CO 3 −K 2 CO 3 . As illustrated in Figure 3a, CO 2 is initially reduced to solid carbon on the steel cathode.…”

“…The overall ZICs performance of carbon materials relies on the proper mesopore structure and surface functional groups, which provide short diffusion paths for enhancing ion and electrolyte transport and pseudocapacitive redox reactions. Surface functionalization of carbons with oxygen-containing functional groups, such as C–OH and CO, is advocated as an ancillary strategy to modulate and amplify the pseudocapacitive behavior of ZICs. , This enhancement occurs through the following reactions: C + X – = X-C (X – : anions) and C–OH + Zn 2+ + 2e = C–O–Zn or C–OH + 2Zn 2+ + e = C–O–Zn + H + . , Although the oxygen-containing carbons have many advantages for ZICs, only a few works about the CO 2 -C were reported. , Li and Yang et al reported a CO 2 -derived OMC for ZICs . OMC was innovatively obtained through bidirectional electrolytic reduction of CO 2 in a molten Li 2 CO 3 –Na 2 CO 3 –K 2 CO 3 .…”

“…A number of studies focusing on capturing and converting CO 2 to highly valuable CO 2 -derived products (for example, carbon monoxide, , urea, , methylamine, formate, − carbon nanotubes (CNTs), porous carbons, defective carbons, nickel-encapsulated octahedral carbons (Ni@OCs), oxygen-rich mesoporous carbons (OMCs), and MoC) were reported to realize decarbonization using CO 2 as a carbon feedstock. In other words, CO 2 can also be used as a valuable carbon source for fabricating useful products.…”