•Chemical and electrochemical corrosion kinetics of PPy in NaOH are identified.•Two corrosion stages are proved to follow first-order kinetics in PPy corrosion.•Dissolved oxygen and concentrations of NaOH play key roles in PPy corrosion.•Chemical and electrochemical processes are mutually promoted in PPy corrosion.The corrosion kinetics of PPy/SO4 in aerated and de-aerated NaOH solutions (0.02–0.5 M) were investigated and the interaction between chemical and electrochemical corrosion processes was verified. The corrosion of PPy is mainly caused by the chemical attack of OH− in de-aerated NaOH, but is accelerated largely in aerated NaOH for the occurrence of the electrochemical processes. These two processes are mutually promoted in aerated NaOH. At a constant NaOH concentration (CNaOH), two corrosion stages are proved to follow first-order kinetics. In each corrosion stage, the chemical and electrochemical processes have different kinetic behavior and CNaOH has important influence on them.

•GO obviously accelerates the H2 evolution in negative plates but PPy impedes it.•Proper PPy/GO (PG) can effectively inhibit the H2 evolution in negative plates.•GO and PG1 (weight ratio of pyrrole to GO = 1:1) largely increase HRPSoC cycle life.•GO and PG1 obviously impede the growth of PbSO4 crystals in negative plates.In order to improve the high-rate partial-state-of-charge (HRPSoC) performance of lead-acid batteries for hybrid-electric vehicles, graphene oxide (GO), polypyrrole (PPy) and three PPy/GO composites with different weight ratio of pyrrole to GO (mpy/mGO) were selected as additives to form negative plates and simulated test cells. The effects of these additives on the electrochemical performance and the microstructure of the negative plate and on the HRPSoC cycle performance of the simulated test cell were investigated. The results indicate that the microstructure of the negative plate is changed with the addition of different additives. GO significantly increases the hydrogen (H2) evolution ability of the negative plate, while PPy has the opposite effect. The incorporation of the proper content of PPy with GO can effectively inhibit the H2 evolution of the negative plate. Moreover, adding different additives in the negative plate also decreases its total impedance, accelerates the redox processes between Pb and PbSO4 on it and increases its specific capacitance. GO and the PPy/GO composite with mpy/mGO = 1:1 (PG1) can significantly increase the HRPSoC cycle life of the simulated test cell. Considering the H2 evolution performance and the HRPSoC cycle performance, the PPy/GO composites with a medium mpy/mGO ratio, such as PG1, may be the appropriate additives for the negative plate of lead-acid batteries.

•Galvanic interactions between polypyrrole and substrate metals were studied.•Polypyrrole generally suffers continuous cathodic polarisation in the couples.•Galvanic couples show unstable state with a poor passivated substrate metal.•Polypyrrole accelerates the corrosion of metals in active dissolution state.In deaerated or aerated 0.1 M NaCl (pH = 1 or 7), galvanic interactions between polypyrrole (PPy) films and different metals (13Cr, NiTi, Pt, Ti and Cu) were investigated in simulated galvanic couples. The PPy suffers cathodic polarisation while the substrate metals (apart from Pt) suffer anodic polarisation. When the substrate metal is inert or well passivated, such as Pt or Ti, there is no galvanic interaction between them. When the substrate metal is in a poor passivation or an active dissolution state, such as 13Cr, NiTi or Cu, the galvanic interactions between them may be strong and cannot be ignored.

•A Polypyrrole/Graphene oxide composite is electro-polymerized with pulse currents.•The effects of pulse current parameters on the capacitance are remarkable.•The composite exhibits a high specific capacitance and good stability.In order to synthesize a PPy/GO composite for supercapacitor applications, a pulse electro-polymerization method was proposed to direct incorporate graphene oxide (GO) into polypyrrole (PPy) films without any additional dopants. The PPy/GO prepared by the pulse electro-polymerization (PC PPy/GO) exhibits a higher specific capacitance. A shorter pulse on time (ton) results in higher specific capacitance, but there is an optimum pulse current amplitude (IA) related to the highest specific capacitance. The PC PPy/GO film (IA = 4 mA cm−2, ton = 50 ms) has a high specific capacitance of 660 F g−1 estimated from galvanostatic charge-discharge in 1 M KCl at a current density of 0.5 mA cm−2. Stability tests for the PPy/GO yield long cycling life up to 1000 cycles with 10% decay in specific capacitance at charge-discharge current density of 10 mA cm−2 in the potential range of -0.5 to 0.5 VSCE.

The effects of continuous cathodic and anodic polarisation on the corrosion of polypyrrole (PPy) films were investigated in neutral 0.1 M NaCl with various electrochemical methods and spectroscopic analyses. With continuous cathodic polarisation, the PPy film nearly maintains the conjugated structure of PPy chains, but loses its electroactivity slightly. With increases in anodic polarisation potential and polarisation time, the electroactivity loss of the polarised PPy film increases rapidly especially at a higher anodic potential; while the damage to the conjugated structure of PPy chains also becomes severer with increasing polarisation time. The mechanisms involved were discussed.Highlights► PPy films nearly keep the conjugated structure after cathodic polarisation. ► PPy films slightly lose their electroactivity after cathodic polarisation. ► PPy films lose more electroactivity with increases in anodic potential and time. ► Cl− attacks PPy to break the conjugated structure at an anodic potential.