o‐Benzenediol‐Functionalized Carbon Nanosheets as Low Self‐Discharge Aqueous Supercapacitors

Abstract

Widening the voltage window is often proposed as a way to increase the energy density of aqueous supercapacitors. However, attempting to operate beyond the aqueous supercapacitor stability region can undermine the supercapacitor reliability due to pronounced electrolyte decomposition, which can lead to a significant self-discharge process. To minimize this challenge, charge injection by grafting o-benzenediol onto the carbon electrode is proposed through a simple electrochemical cycling technique. Due to charge injection from o-benzenediol into the carbon electrode, the equilibrium potential of the individual electrode can be reduced. In addition, due to its small molecular size, charge distribution, which is commonly faced by bulk pseudocapacitive materials, is also avoided. The assembled supercapacitor based on the o-benzenediol-grafted carbon demonstrated a maximum energy density of 24 Wh kg and a maximum power density of 69 kW kg , with a retention of 89 % after 10 000 cycles at 10 A g . A low self-discharge of about 4 h was recorded; this could be attributed to the low driving force arising from the lower equilibrium potential. Thus, the proposed technique may provide insight towards the tuning of the equilibrium potential to attain reliable, high-performing supercapacitors with a low self-discharge process.

Synergistic Interface‐Assisted Electrode–Electrolyte Coupling Toward Advanced Charge Storage

“…The HCO-PFC//FG full cell, retaining 38% of full energy after 4.7 h resting, i.e., η R (4.7 h) = 38%, exhibited significantly reduced self-discharge than that of the CO-PFC//FG full cell, reserving only 24% of full energy after 1.5 h resting. Additionally, the selfdischarge rate of the HCO-PFC//FG full cell device is also lower than or comparable to those of recently reported RE-based SCs, such as NDC redox cell (η R (4 h) = 25%), [36] graphene-HQ/H 2 SO 4 cell (η R (1.5 h) = 14%), [37] EV/TBA/Br cell (η R (6 h) = 45%), [38] and even nonaqueous rGO-biredox ionic liquid (IL) cell (η R (4.4 h) = 40%). [10] Importantly, given that the self-discharge rate could be aggravated in large voltage window, the high energy remaining ratio for the 1.8 V HCO-PFC//FG full cell device is particularly encouraging as compared to those of the reported devices within working voltages less than 1.4 V. [39][40][41] Moreover, the achieved self-discharge rate for the HCO-PFC//FG cell is partially influenced by the FG anode with a fast self-discharge rate.…”

In Situ Hard‐Template Synthesis of Hollow Bowl‐Like Carbon: A Potential Versatile Platform for Sodium and Zinc Ion Capacitors

“…The open-circuit voltage drops to 2.84 V after 100 h, corresponding to a 29% loss, and a self-discharge rate of 11.6 mV h −1 . This rate is lower than many other capacitor devices (Figure 6e), [60][61][62][63][64][65][66][67] including the graphene-based EDLC (156 mV h −1 ), [62] B-Si/SiO 2 /C-based lithium ion capacitor (14.4 mV h −1 ) [15] and MoS 2 @PEDOT-based SIC (15 mV h −1 ). This implies stable electrode surfaces at the test potential.…”

Progress of Two‐Dimensional Ti3C2Tx in Supercapacitors

“…The voltage of the Ti 3 C 2 T x //α‐MnO 2 cell fades from 2.2 to 1.5 V in 30 000 s, which can be quantified as a 32 % reduction in the open‐circuit voltage. A comparison of the self‐discharge behavior between Ti 3 C 2 T x ‐ and carbon‐based SCs is shown in Figure . It can be seen that the reported values of Ti 3 C 2 T x ‐based SCs exhibit lower discharge rates and better voltage retentions than those of most carbon‐based SCs; this can be attributed to the hydrophilic surface arising from terminated functional groups (−OH and −O) and the ultrahigh metallic conductivity of Ti 3 C 2 T x .…”

“…Acomparison of the self-discharge behavior between Ti 3 C 2 T x -a nd carbon-based SCs is shown in Figure 27. [144,[160][161][162][163][164][165][166][167][168][169][170][171][172][173][174] It can be seen that the reported values of Ti 3 C 2 T x -based SCs exhibit lower discharge rates and better voltage retentions than those of most carbon-based SCs;t his can be attributed to the hydrophilic surface arising from terminated functional groups (ÀOH and ÀO) and the ultrahigh metallic conductivity of Ti 3 C 2 T x .G oode lectrolyte-electrode contact, which benefits from the excellenth ydrophilicity of Ti 3 C 2 T x ,c an enhancet he accessibility of the electrolyte to the active surface and accelerate chargetransfer.However, the self-discharge mechanism based on Ti 3 C 2 T x -based SCs has barely been studied and still needs to be explored.…”