Preparation and Investigation of Synthetic Carbon Nanosheets and Copper (II)-Polydopamine for Hydrogen Production

Abstract

The development of efficient co-catalysts indicates one of the most significant topics for the commercialization of photoelectrochemical hydrogen evolution. The design and preparation of carbon-based catalysts is a significant research part for inexpensive, environment-friendly, and durable catalysts that may replace previously developed noble metal catalysts. Nevertheless, the challenge associated with the previous carbon-based catalysts, such as graphene and graphene-based materials, lies in the complicated and inefficient synthetic processes. As the simplest model carbon-based platform, CVD-monolayer graphene was chosen as a HER catalyst. Graphene possesses excellent transmittance and superior intrinsic carrier mobility. For the first time, we have investigated new possibilities of monolayer graphene as the efficient HER catalyst. The catalytic activity can be further enhanced by generating more active sites. Treatment with N2 plasma also induces N doping and abundant defects. The catalyst exhibits a lower Tafel slope (45 mV/decade) and a higher exchange current density (7.1×10-5 mA/cm2) than those of other previously reported carbon-based HER catalysts, indicating performance comparable to that of Pt catalyst. Based on the electrochemical analysis, the active sites of the N-doped graphene have been identified and quantified. Moreover, another type of the biomimetic carbon-based nanosheets is addressed as a new HER catalyst. Here, inspired by biomolecular system based on mussel adhesive protein, we prepared transition metal-complexed PDA matrix (M-PDA) as a new hydrogen evolution catalyst and investigated HER catalytic properties in neutral pH condition. Through oxidative polymerization of dopamine, we synthesized PDA with various transition metal such as Co2+, Cu2+, Mn2+, Ni2+, and Fe3+ ion. Moreover, Cu(II)-PDA complex show the lowest overpotential for HER among these M-PDAs. To the best of our knowledge, there is no previous studies on the application of biomimetic PDA derivatives to hydrogen production catalysts, and the overpotential of Cu(II)-PDA is lowest value among copper-based electrocatalysts for hydrogen production. This significant enhancement achieved in this study emphasizes the new possibilities for the application of bioinspired materials as hydrogen evolution reaction catalyst as well as molecular precursor approach.