Data on a highly stable electrocatalyst of NiCoPt/Graphene-dot nanosponge for efficient hydrogen evolution reaction

The data presented in this article are related to the research article entitled “NiCoPt/Graphene-dot Nanosponge as a Highly Stable Electrocatalyst for Efficient Hydrogen Evolution Reaction in Acidic Electrolyte (N.-A. Nguyen et al., 2020) [1]. This article reports a simple method to synthesize NiCoPt/Graphene-dot as an electrocatalyst with low Pt loading but high hydrogen evolution reaction (HER) performance. The morphology of NiCoPt/Graphene-dot was analyzed by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) techniques. The structural and chemical properties of NiCoPt/Graphene-dot were investigated by using X-ray Powder Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques.


Specifications
Physics, Chemistry Specific subject area Electrochemical catalysts for hydrogen evolution reaction Type of data Table  Image Graph Figure  How

Data Description
The data of this article provides information on the synthesis of Ni 48 Co 48 Pt 4 alloy wrapped with graphene dots, which shows the high HER performance as well as very stable in the longterm of hydrogen production. Fig. 1 gives a synthesis process of Ni 48 Co 48 Pt 4 /Graphene-dot (mentioned as Ni 48 Co 48 Pt 4 /G-dot). Fig. 2 presents the morphology and structure of Ni 48 Co 48 Pt 4 /G-dot and Ni 48 Co 48 Pt 4 nanoalloy. Fig. 3 shows the morphology and lattice fringes with inter-planner    Fig. 4 supplies the survey XPS spectrum to disclose the electronic structure of Ni 48 Co 48 Pt 4 /G-dot. Table 1 indicates the detailed values of electrochemical performance in the hydrogen evolution reaction (HER) application.
After synthesizing Ni 48 Co 48 Pt 4 /G-dot sample as described in Figure 1 , the morphology and structure of obtained catalysts were investigated as seen in Fig. 2 . Clearly, in the presence of C-dots in the synthesis process, the morphology of Ni 48 Co 48 Pt 4 /G-dot is sponge-like in contrast to Ni 48 Co 48 Pt 4 nanoalloy (synthesized without C-dots) with nanoparticles that tend to be aggregated ( Fig. 2 a, b). Fig. 2 c shows the XRD patterns of Ni 48 Co 48 Pt 4 /G-dot and Ni 48 Co 48 Pt 4 nanoalloy samples. In detail, the pattern of Ni 48 Co 48 Pt 4 /G-dot nanosponge, a weak and broad peak at approximately 24.35 ˚representing the crystal plane of (002) is observed. However, no peak is found at 24.35 ˚in the pattern of Ni 48 Co 48 Pt 4 nanoalloy. The obtained result indicates the formation of graphene layers in Ni 48 Co 48 Pt 4 /G-dot, which wraps the synthesized catalyst and creates a sponge-like polycrystalline structure [2] . The morphology of Ni 48 Co 48 Pt 4 /G-dot nanosponge is confirmed again by TEM as seen in Fig. 3 a. The nanoparticles wrapped by graphene layers are clearly seen in Fig. 3 b. Fig. 4 shows the survey XPS spectrum of Ni 48 Co 48 Pt 4 /G-dot nanosponge, which was treated under a mild acceleration Ar + energy of 0.5 keV. The high-resolution of Ni2p, Co 2p, Pt4f, and C1s spectra are deconvoluted as seen in the reference [1] . As a result, the carbon amount has recorded of 25.43 at%, suggesting that the surface of the nanoparticle is enriched with carbon. On the other hand, atomic percentages of metal elements obtained from survey spectra taken from Ni 48 Co 48 Pt 4 /G-dot nanosponge are given with 86.69 % of atomic percentage for Pt while only 7.14 and 6.17% are found for Co and Ni. The top layer is enriched up to 86.69% Pt suggesting that the surface composition of an alloy is controlled by the tendency of Pt metal segregates towards the surface. This result can be used to explain why the HER performance of Ni 48 Co 48 Pt 4 /G-dot nanosponge is excellent as seen in Table 1 .
The beneficial effect of graphene-dot wrapped nanosponge on the HER activity is proven by direct comparison of the HER performance of the Ni 48 Co 48 Pt 4 with and without G-dots as seen in Table 1 . The overpotential value of 52.70 mV for Ni 48 Co 48 Pt 4 nanoalloy is higher than that of Ni 48 Co 48 Pt 4 /G-dot (45.54 mV) to obtain a current density of 10 mA.cm −2 . The obtained data prove that the coverage of the nanoparticles with G-dots not only enhances durability but also increases its electrical conductivity and provides a favorable catalyst/electrolyte interface for electron transfer from the electrode to the protons in the electrolyte.
The beneficial impact of the G-dot is further confirmed by the EIS, Tafel plots, and the double layer capacitance analysis. The Tafel slope of Ni 48 Co 48 Pt 4 /G-dot is 33.90 (mV/dec), which is smaller than the slope of 37.62 mV/dec recorded for Ni 48 Co 48 Pt 4 nanoalloy. This data suggests that the electrochemical recombination step is the rate-determining step and the reaction follows the Volmer-Tafel mechanism [3][4][5] . The ECSA of Ni 48 Co 48 Pt 4 /G-dot is 57.51 cm 2 , which is larger than that of 45.71 cm 2 of Ni 48 Co 48 Pt 4 nanoalloy. In addition, the smaller value of 29.05 for R ct is fitted for the Ni 48 Co 48 Pt 4 /G-dot compared to the R ct of 47.15 recorded for Ni 48 Co 48 Pt 4 nanoalloy, suggesting a more effective charge transfer across the catalyst/electrolyte interface that promotes the electrochemical reaction.
The comparative chronoamperometric curves recorded for Ni 48 Co 48 Pt 4 alloy and Ni 48 Co 48 Pt 4 /G-dot are given in the reference [1] . The 40% loss of current density after 18 h of operation was recorded for Ni 48 Co 48 Pt 4 nanoalloy, whereas Ni 48 Co 48 Pt 4 /G-dot nanosponge retains 94% of the current density after 21 h, showing an excellent catalytic activity. The result illustrates the positive impact of the G-dot in the stability of Ni 48 Co 48 Pt 4 /G-dot catalyst in acidic electrolyte.

Methods
NiCoPt/Graphene-dots (referred to as NiCoPt/G-dot) were synthesized from the mixed precursor solutions and carbon dots (C-dots). C-dots were synthesized using a procedure developed in our previous work [ 2 , 6 , 7 ]. A typical synthesis for the Ni 48 Co 48 Pt 4 /G-dot nanohybrid can be described as seen in Fig. 1 . Ni 48 Co 48 Pt 4 nanoalloy was synthesized with the same method to obtain NiCoPt/G-dot except using C-dots.

Experimental design
After synthesizing Ni 48 Co 48 Pt 4 /G-dot and Ni 48 Co 48 Pt 4 nanoalloy samples, their physical characteristics such as crystalline structure, morphology, and surface chemical state were analyzed by using techniques such as the Powder X-ray diffraction (XRD), the scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. In more detail, an X-ray diffractometer (Smart Lab, λ = 1.5406 Å , Cu K α radiation, Rigaku corporation) was used to analyze the crystalline structure of the NiCoPt/Gdot nanosponge. Scanning electron microscopy (FE-SEM, Hitachi S-4800 with UHR lens) and high-resolution transmission electron microscopy (HRTEM, JEM-2100 F, 200 kV, JEOL LTD., Japan) were used to analyze the morphology of the synthesized NiCoPt/G-dot nanosponge. X-ray photoelectron spectroscopy (XPS) using a Thermo Fisher Theta Probe system equipped with a monochromated Al-K X-ray source with a photon energy of 1486.6 eV (K-Alpha + , Thermo Fisher Scientific) was used to analyze the surface chemical state of synthesized sample.
For measuring the electrochemical performance of the NiCoPt/G-dot catalyst, a threeelectrode scheme with a rotating disc electrode was employed, using a potentiostat (IviumStat electrochemical analyzer from Ivium Technologies, Netherlands). NiCoPt/G-dot catalyst coated on glassy carbon (GC) electrode was used as the working electrode (WE). A platinum coil and a Ag/AgCl (NaCl 3 M) electrode were used as the counter and reference electrodes, respectively. The electrochemical catalytic activity of the NiCoPt/G-dot was performed in the acidic electrolyte (0.5 M H 2 SO 4 ) by linear sweep voltammetry (LSV) at a scan rate of 10 mV/s. The electrolyte was degassed by bubbling with ultra-pure nitrogen gas for 30 min before the measurements. The electrochemical impedance spectroscopy (EIS) was examined at a voltage of -0.20 V vs a reversible hydrogen electrode (RHE) in a frequency range of 0.1 to 10 5 Hz.

Ethics Statement
The data resulted from experimental neither on animal models nor with human volunteers.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships which have, or could be perceived to have, influenced the work reported in this article.