No abstract

We report here non‐enzymatic electrochemical biosensing of H2O2 using a highly stable, metal‐free, tyramine functionalized graphene (T‐GO) based electrocatalytic system. The surface functionalization of tyramine on graphene was carried out chemically. The obtained sheets were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD) as well as X‐ray photoelectron (XP), Raman, FT‐IR and UV‐visible spectroscopy. More significantly, the combined results from morphological and structural studies show the formation of a few layers of graphene with effective large‐scale functionalization by tyramine. As a metal‐free electrocatalyst, the as‐synthesized T‐GO shown good electrocatalytic activity towards reduction of H2O2 with a sensitivity of 0.105 mM/cm2 confirmed by combined results from cyclic voltammetric (CV) and linear sweep voltammetric (LSV), and amperometric (i–t) measurements. The lower onset potential (−0.23 mV vs SCE), lower detection limit, wider concentration range (10 mM to 60 mM) with higher electrochemical current and potential stability demonstrated the potential of our non‐enzymatic and cost‐effective T‐GO based electrocatalytic system towards reduction of hydrogen peroxide.

In this study, we report a method for fabrication of rhodium nanoparticles decorated on graphene oxide (Rh–GO) with high coverage of active sites of Rh nanospheres (NSs) on GO. It is one of the most pivotal aspects in the development of novel systems having high electrocatalytic performance toward overall water splitting reactions and is found to be better than universally acceptable Pt-based nanoelectrodes. The synthesis of nanohybrids shows the well-dispersed Rh NSs (∼50 nm) on a few layers of graphene oxide sheets. These as-synthesized nanomaterials were confirmed by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, Brunauer–Emmett–Teller (BET) surface area measurements, thermogravimetric analysis (TGA), and X-ray diffraction (XRD) analysis. Furthermore, Rh–GO exhibits significantly improved electrochemical performance toward electrocatalytic water splitting reactions, that is, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and it shows exceptionally an ultrasmall overpotential of 2 mV for the HER, reaching a current density of 10 mA cm–2 with a smaller Tafel slope 10 mV dec–1, and the OER overpotential reaches 0.23 V at 10 mA cm–2 with a Tafel slope of 27 mV dec–1. The reduced charge transfer resistances after Rh NSs decoration on GO which lead to simultaneous enhancement in feasibility toward interfacial electron transfer, result in an increase in activity toward overall water splitting reactions (both HER and OER).

Cu 2 ZnSnS 4 (CZTS) was synthesized by the sonochemical method using 2-methoxyethanol as the solvent and subsequently decorated onto graphene oxide (GO synthesized by the modified Hummers’ method) using two different approaches such as in situ growth and ex situ synthesis followed by deposition. Preliminary characterizations indicated that the synthesized CZTS belongs to the kesterite structure with a sphere-like morphology. The in situ-synthesized CZTS/GO (I-CZTS/GO) composite is used as an efficient electrocatalyst for hydrogen evolution reaction (HER) which revealed superior electrocatalytic activity with a reduced overpotential (39.3 mV at 2 mA cm –2 ), Tafel slope (70 mV dec –1 ), a larger exchange current density of 908 mA cm –2 , and charge transfer resistance (5 Ω), significantly different from pure CZTS. Besides, the I-CZTS/GO composite exhibits highest HER performance with high current stability of which shows no noticeable degradation after i – t amperometry. The catalytic activity demonstrates that the I-CZTS/GO composite could be a promising electrocatalyst in hydrogen production from their cooperative interactions.

A simple one-step chemical method is employed for the successful synthesis of CuO(50%)–ZnO(50%) nanocomposites (NCs) and investigation of their gas sensing properties. The X-ray diffraction studies revealed that these CuO–ZnO NCs display a hexagonal wurtzite-type crystal structure. The average width of 50–100 nm and length of 200–600 nm of the NCs were confirmed by transmission electron microscopic images, and the 1:1 proportion of Cu and Zn composition was confirmed by energy-dispersive spectra, i.e., CuO(50%)–ZnO(50%) NC studies. The CuO(50%)–ZnO(50%) NCs exhibit superior gas sensing performance with outstanding selectivity toward NO2 gas at a working temperature of 200 °C. Moreover, these NCs were used for the indirect evaluation of NO2 via electrochemical detection of NO2– (as NO2 converts into NO2– once it reacts with moisture, resulting into acid rain, i.e., indirect evaluation of NO2). As compared with other known modified electrodes, CuO(50%)–ZnO(50%) NCs show an apparent oxidation of NO2– with a larger peak current for a wider linear range of nitrite concentration from 20 to 100 mM. We thus demonstrate that the as-synthesized CuO(50%)–ZnO(50%) NCs act as a promising low-cost NO2 sensor and further confirm their potential toward tunable gas sensors (electrochemical and solid state) (Scheme 1).