Metal-Free Polyaniline Copolymers: An Efficient and Stable Electrocatalyst for Clean Hydrogen in Acidic Media

In this work, we explore the electrochemical hydrogen evolution reaction (HER) properties of metal-free polyaniline homopolymer and copolymers synthesized via the chemical polymerization route. The as-prepared polyaniline (PANI) homopolymer, poly (aniline-co-3-aminobenzoic acid) (P(ANI-co-ABA), poly (aniline-co-triphenylaniline) (P(ANI-co-TPA) and poly (aniline-co-3-nitroaniline) (P(ANI-co-3NI) were characterized and interrogated using several analytical techniques. The FTIR and XRD analyses revealed similar resemblance between PANI homopolymer and copolymers, suggesting that the polymer backbone were not disrupted during copolymerization. Furthermore, the reduction in optical band gap for P(ANI-co-3NI) means that the said copolymer exhibits higher electrical conductivity, which is of great importance for HER applications. In contrast, the HER performance of the as-prepared polymers were evaluated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The highly conductive P(ANI-co-3NI) exhibited superior HER performance with higher surface coverage, electrochemical surface area and faster kinetics as compared to other as-prepared polymers. Moreover, P(ANI-co-3NI) copolymer possessed Tafel slope of 47.9 mV.dec -1 and turnover frequency (TOF) of 3 mmol H 2 .s -1 which are noticeable higher HER performance than that of PANI homopolymer (Tafel slope of 64.6 mV.dec -1 and TOF OF 0.25 mmol H 2 .s -1 ). This study provides an efficient route for the development of metal-free electrocatalyst with excellent HER performance.