•In ionic liquid, CV of 1,4-dinitrobenzene shows only one redox wave and undergoes two-step one-electron process.•Ion-pairing forms between the electrochemical products of 1,4-dinitrobenzene and cation in ionic liquid.•The interaction of hydrogen-bonding is much stronger than the interaction of ion-pairing.The electrochemical reduction of 1,4-dinitrobenzene (PNB) in ionic liquid (BMIMPF6 and HMIMPF6) has been studied by cyclic voltammetry (CV) and IR spectroelectrochemistry. In ionic liquid, only one couple of redox peak is observed, but the results obtained from IR spectroelectrochemistry support the existence of intermediate (PNB−) in ionic liquid, hence it is reduced in two-step one-electron transfer. The results obtained in mixed media (CH3CN with ionic liquids) suggest that the electrochemical products (radical anion PNB− and dianion PNB2 −) can form strong ion-pairing with the cation of ionic liquid, and the interaction between the electrochemical products and BMIM+ is much stronger than HMIM+. In proton donors mixed media (ionic liquid with ethanol), the interaction of hydrogen-bonding between the electrochemical products and ethanol is much stronger than the interaction of ion-pairing between the electrochemical products and the cation of ionic liquid.

•Firstly, the secondary amines were oxidized to secondary amines radical cation.•Secondly, the terminal primary amines were oxidized to amino radical cation.•Thirdly, the terminal hydroxyl groups were oxidized to the phenol radical.•The polaronic polyaniline was further oxidized to the bipolaronic polyaniline.•The bipolaronic polyaniline turns to quinoid structure by deprotonation.The redox mechanism of polyaniline (PANI) film in acid solution was studied by in situ rapid-scan time-resolved infrared spectroelectrochemistry (RS-TR-FTIRS) method. In the potential rang between −0.29 and 0.91 V, there are four pairs of redox peaks. These four pairs of redox peaks were minutely investigated by cyclic voltammetry (CV) and in-situ infrared spectroelectrochemistry. The results illustrated that the first pair of redox peaks are according to oxidation of the secondary amines in the middle of molecular PANI chain, the second pair of redox peaks are according to oxidation of terminal primary amines, the third pair of redox peaks are according to oxidation of terminal hydroxyl groups, the forth pair of redox peaks are according to oxidation of the polaronic PANI to the bipolaronic PANI. The bipolaronic PANI completely turns to quinoid structure with highly conjugated by deprotonation when the electrode potential was higher than 0.71 V. Meanwhile, the hydrogen bonding between the oxidation products of PANI and water molecules disappeared.

A simple and sensitive electrochemical method for the simultaneous detection of hydroquinone (HQ) and catechol (CC) was developed, based on a multi-walled carbon nanotube and MnO2 nanowire composite (MWCNTs–MnO2) modified glassy carbon electrode (GCE). Electrochemical impedance spectra studies showed a small charge transfer resistance (Rct) for the MWCNTs–MnO2 composite film due to the incorporation of MWCNTs. Compared with the bare GCE, both HQ and CC exhibited well-defined redox peaks and much larger peak currents at MWCNTs–MnO2/GCE, which was related to the higher specific surface area and catalysis rate of the MWCNTs–MnO2 film. The MnO2 film acted as an electron transfer mediator to accelerate the electron transfer rate for the oxidation of HQ and CC. Due to the large separation of oxidation peak potentials (102 mV), the concentrations of HQ and CC can be easily determined simultaneously. The oxidation peak currents were linear to HQ/CC in the range from 5 × 10−7 to 8 × 10−5 M with the detection limits of 5 × 10−8 M (S/N = 3) for HQ and 8 × 10−8 M (S/N = 3) for CC. Simultaneous determination of HQ and CC with such an electrode was conducted in tap water samples with reliable recovery.

The synthesis of polyaniline/platinum microelectrodes (PPME) have been achieved for the first time by using the controlled electrochemical reduction of PtCl62−. First, the PANI film was electrochemical prepared on the glass carbon electrode (GCE) surface by using the method of CV. It was found that the PANI film is composed of 100–200 nm diameter rods. Then, the electrochemical reduction of PtCl62− on the PANI modified surface was carried out and Pt particle was about 300–600 nm in diameter on the end of PANI membranes. Electrochemical experiments show that the microelectrodes have superior catalytic performance toward formaldehyde and methanol electrochemical oxidation.

A simple and sensitive electrochemical method for the simultaneous detection of hydroquinone (HQ) and catechol (CC) was developed, based on a multi-walled carbon nanotube and MnO2 nanowire composite (MWCNTs–MnO2) modified glassy carbon electrode (GCE). Electrochemical impedance spectra studies showed a small charge transfer resistance (Rct) for the MWCNTs–MnO2 composite film due to the incorporation of MWCNTs. Compared with the bare GCE, both HQ and CC exhibited well-defined redox peaks and much larger peak currents at MWCNTs–MnO2/GCE, which was related to the higher specific surface area and catalysis rate of the MWCNTs–MnO2 film. The MnO2 film acted as an electron transfer mediator to accelerate the electron transfer rate for the oxidation of HQ and CC. Due to the large separation of oxidation peak potentials (102 mV), the concentrations of HQ and CC can be easily determined simultaneously. The oxidation peak currents were linear to HQ/CC in the range from 5 × 10−7 to 8 × 10−5 M with the detection limits of 5 × 10−8 M (S/N = 3) for HQ and 8 × 10−8 M (S/N = 3) for CC. Simultaneous determination of HQ and CC with such an electrode was conducted in tap water samples with reliable recovery.