Graphene-based nanosheets have gained prominence in batteries and super-capacitors owing to their high aspect ratio, tunable transport properties, diverse ionic functionalities, and variable surface characteristics. Variants like pristine graphene, graphene oxide, or chemically/thermally reduced graphene are not equal in ionic and transport properties owing to the presence or grafting of functional groups in the honeycomb carbon structure. Therefore, the conductivity or ionic functionality are synergistic in providing the combination of properties needed to function in energy systems or electronics. This research enhances the performance of lead acid battery using three graphene variants and demonstrates the in-situ electrochemical reduction of graphene. Using lead-based electrodes, t...[ Read more ]

Graphene-based nanosheets have gained prominence in batteries and super-capacitors owing to their high aspect ratio, tunable transport properties, diverse ionic functionalities, and variable surface characteristics. Variants like pristine graphene, graphene oxide, or chemically/thermally reduced graphene are not equal in ionic and transport properties owing to the presence or grafting of functional groups in the honeycomb carbon structure. Therefore, the conductivity or ionic functionality are synergistic in providing the combination of properties needed to function in energy systems or electronics. This research enhances the performance of lead acid battery using three graphene variants and demonstrates the in-situ electrochemical reduction of graphene. Using lead-based electrodes, this is the first study of electrochemical reduction of graphene oxide with the having very high electronic and dielectric properties for optoelectronic and advanced electrode applications.

Technological demands in hybrid electric vehicles, large scale storage and portable power stations has furthered more research interests in Lead Acid Batteries (LAB), in addition to the advantage of power rating per cost. The LAB positive active materials (PAM), due to low utilization and life cycle, severely limits the competitiveness of the traditional battery. The combination of cathode materials with tailored graphene based additives: Graphene Oxide (GO-PAM), chemically converted graphene (CCG-PAM) and pristine graphene (GX-PAM) resulted in improved discharge capacity and cycle life. GO-PAM had the best performance with the highest utilization of 41.8%, followed by CCG-PAM (37.7%), control-PAM (29.7%), and GX-PAM (28.7%) at 2.5C rate. CCG-PAM had better charging performance such as lower internal resistance, but poorer cycle life compared to GO-PAM. Cycled at 2.5C rate, all samples but the control, had increasing capacity till after ~50 cycles. Graphene/PbO₂ electrochemical reactions and better inter-particle cohesion enhanced the utilization of cathode material. Ion transfer model was developed showing the optimization of ion transfer mechanisms in the gel (intermediate) zone. The mechanistic interfacial characteristics of graphene enhancements in LABs were further evaluated based on the capacitance of the double layer (C_dl) and charge transfer resistance (R_ct). The electrochemical impedance spectroscopy (EIS) curves were obtained from Pb/PbO₂/HgSO₄ system and evaluated using the Randles EIS circuit model, while Randles-Sevcik Equation aided the understanding the cyclic voltametry (CV). Enhanced samples had lower R_ct, and were marked by increased peak current values indicating increased faradaic and non-faradaic capacitances.

Graphene-based papers have high mechanical strength and they are suitable for large-scale electronics. This work established the ex-situ electrochemical reduction and transition in the chemistry, electrical and fracture properties of graphene oxide paper (GO) at the anode (aERGO) and cathode (cERGO) of a lead-based electrode system. Higher thermal stability and lower weight loss of aERGO (34wt% at 800 °C) with XRD peak at 2ϴ = 10.5° showed the reduction of the ordinary GO paper (95wt% at 800 °C). The SEM fracture surfaces showed that the cERGO failed by ductile rupture of a higher degree than the ordinary GO paper due to corrugation of graphene clusters, while that of the aERGO was far less ductile. The UV-Vis, FT-IR and XPS showed the removal of functional groups, via the interaction of graphene oxide functional groups with protons, adsorbed oxygen containing ions. The aERGO and cERGO showed superior electrical conductivities of 1.61 x 10⁶ S/m and 4.27 X 10⁵ S/m respectively. The temperature and frequency dependent electronic characteristics of electrochemically reduced graphene paper (ERGO) were compared with those of graphene oxide paper (GO). The conductivity, permittivity and dielectric losses in ERGO papers were clearly leading those of GO paper by ~2 order of magnitude. Strongly polarized and ionized cloud of charge carriers in the ERGOs were due to higher concentration of corrugated conductive clusters, which functioned as a plethora of nano-capacitor manifolds. Frequency dependent properties were governed by dipole mobility, while temperature dependent electronic characteristics were governed by charge-carriers thermal activation and residence time, and increase in size of sp2 clusters concentration.