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The effective Ni–Cu bimetallic nanocomposite was deposited on a glassy carbon electrode, GCE, that modified with carbon quantum dots, CQDs. The deposition process was done by one-step and controllable electrochemical method in an electrolyte of nickel and copper sulfate. The structural properties of composite studied by techniques such as X-ray diffraction, XRD, energy dispersive X-ray analysis, EDX, field emission scanning electron microscopy, FESEM, and transmission electron microscopy, TEM. Ni–Cu/RCQDs nanocomposite was applied as a cathode for catalysis of hydrogen evolution reaction, HER, in acidic media by cyclic voltammetry, CV, linear sweep voltammetry, LSV, chronoamperometry, CA, and electrochemical impedance spectroscopy, EIS. The onset potential, E onset , for the evolution of hydrogen at the current density of −10 mA cm−2 for Ni–Cu/RCQDs was −230 mV vs. SHE that had a 100 mV shift to positive voltages in comparison with Ni–Cu catalyst. It can be related to the synergistic effect between metallic nanoparticles. V. dec−1, respectively. Image 1 • CQDs were synthesized by facile and one-step electrochemical method. • One-step electrochemical method was employed for deposition of CQDs. • A green, low-cost and electrochemically-synthesized electrocatalyst was introduced. • Enhancement of hydrogen evolution reaction was evaluated. • The Ni-Cu/RCQD nanocomposite, offers promising option as cathodic electrode for HER. [ABSTRACT FROM AUTHOR]

• CQDs were synthesized by facile and affordable electrochemical method • One step electrochemical method was employed to synthesis and deposition of electrodes. • CQDs caused to enhanced active surface area for deposition of metal nanoparticles. • The Pd-NPs/RCQD nanocomposite, offers promising option for wide catalytic applications such as high stability, low activation energy, high current density and good electric conductivity for MOR and HER. Glassy carbon electrode, GCE, is decorated with an electrochemically-deposited layer of reduced carbon quantum dots, RCQDs. The Pd nanoparticles are then electrodeposited on RCQDs and the Pd-NPs/RCQDs/GCE is fabricated. The fabricated electrodes are characterized by some characterization techniques. The electrocatalytic performance of the electrodes for methanol oxidation reaction, MOR, and hydrogen evolution reaction, HER, are investigated using different electrochemical measurement techniques in alkaline and acidic media, respectivly. Cyclic voltammetry, CV, Linear sweep voltammetry, LSV, Chronoamperometry, CA, and electrochemical impedance spectroscopy, EIS, measurements are used to evaluate the bifunctional catalytic behavior of the Pd-NPs/RCQDs/GCE. All results are compared with Pd-NPs/GCE and the effect of decorating the GCE substrate with RCQDs is discussed. The results indicate that modification of GCE with a layer of RCQDs increases the active surface area from 0.12 for Pd-NPs/GCE to 0.22 cm2 for Pd-NPs/RCQDs/GCE. Also E onset and EIS parameters are calculated. [ABSTRACT FROM AUTHOR]

• CQDs were synthesized by facile and cost-effective electrochemical method. • CQDs that deposited by one step electrochemical method, caused to increases of electrochemical active surface area and good dispersion of nanoparticles on it. • A green, low-cost and electrochemically-synthesized electrocatalyst was introduced. • The Ni-NPs/RCQD nanocomposite as a novel non-platinum catalyst, offers promising option for wide catalytic applications. The methanol oxidation reaction (MOR) is catalyzed by non- platinum catalysts of nickel nanoparticles (Ni-NPs) that deposited on a modified glassy carbon electrode by reduced carbon quantum dots (RCQD). The cyclic voltammetry (CV), and chronoamperometry (CA) techniques are used for the electrodeposition process. Then the morphology and structure of electrodeposited materials are characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and scanning electron microscopy (SEM). Results showed that Ni-NPs are homogeneously electrodeposited on the surface of CQDs. Also, the catalysis of MOR on electrodes is investigated by different electrochemical techniques like CV and CA, and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of electrodes for MOR has been informed with several parameters. For example, for Ni-NPs/RCQDs/GCE, the peak current density at E = 0.56 V, vs. Ag/AgCl was 32 mA·cm−2 that is higher than of Ni-NPs/GCE. Also, the this catalyst shows excellent stability and high current at constant voltage. [ABSTRACT FROM AUTHOR]