Gold nanoparticles decorated covalent organic polymer as a bimodal catalyst for total water splitting and nitro compound reduction

The design and construction of a bimodal catalyst with magnificent performance and high stability is a debatable one for total water splitting and nitro compound reduction. Herein, we report the synthesis of a covalent organic polymer network based on 1,4-phenylenediamine based covalent organic polymer (PD-COP) and its decoration with Au nanoparticles (Au NPs) as well as their confirmation using various analytical and surface techniques. The electrocatalytic activity toward total water-splitting reaction (OER and HER) in KOH solution (1.0 M) was investigated. In addition, the reduction of aromatic nitro compounds (4-nitrophenol (4-NP) and 2-nitroaniline (2-NA)) was carried out in the presence of NaBH4. Among the different electrocatalysts (PD-COP, Au@PD-COP-I, Au@PD-COP-II, Au@PD-COP-III and Au@PD-COP-IV) studied in this work, the Au@PD-COP-II demands a low overpotential of 288 mV and 184 mV to attain a 50-mA/cm2 geometrical current density with a lowest Tafel slope value of 56 and 85 mV/dec for OER and HER respectively. From the OER and HER phenomenal activity, a two-electrode system was constructed, and it needs a cell voltage of 1.615 V to conquer a current density of 10 mA/cm2 with outstanding stability for 34 h. The high electroactivity of Au@PD-COP-II may be allied with the presence of innumerable redox-active sites and high electrochemical active surface area (ECSA) towards effective water electrolysis. Further, the catalytic activity performed towards the reduction of 4-NP to 4-aminophenol (4-AP) and 2-NA to o-PDA (o-phenylenediamine), Au@PD-COP-II showed good catalytic activity with a reduction time of 20 and 14 min respectively.