Non-noble-metal Ni nanoparticles modified N-doped g-C3N4 for efficient photocatalytic hydrogen evolution

https://doi.org/10.1016/j.ijhydene.2019.09.129Get rights and content

Highlights

  • Ni nanoparticles were loaded on the surface of N-doped g-C3N4 by photodeposition.

  • This material exhibits better photocatalytic activity than Pt@N-doped g-C3N4.

  • Our study offers an alternative method to achieve the cheap photocatalyst for HER.

Abstract

The use of non-noble-metal to replace precious metal as co-catalyst in solar-driven hydrogen evolution reaction (HER) is important for lowering hydrogen production cost. In this work, nickel metal nanoparticles loaded nitrogen-doped graphite carbon nitride (NiNCN3) was prepared, which significantly enhanced the HER activity of nitrogen-doped graphite carbon nitride. The hydrogen evolution rate of NiNCN3 can reach to 1507 μmol g−1 h−1, much higher than that of 3 wt % Pt/NCN (1055 μmol g−1 h−1). The distinguished photocatalytic performance is due to the accelerated electron transfer efficiency and inhibited photogenerated electron-hole recombination. Our study offers an alternative method to achieve the low-cost and effective noble-metal-free photocatalyst for HER.

Graphical abstract

A noble-metal-free photocatalyst for hydrogen evolution was prepared by photodeposition of Ni metal particles on the surface of nitrogen-doped graphitic carbon nitride. This material exhibits excellent photocatalytic activity, which provide an alternative choice to avoid using Pt as a co-catalyst.

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Introduction

The development of society is closely linked to energy supply. However, the excessive consumption of fossil energy has caused serious energy crisis and environmental problems [1,2]. Therefore, researchers are making great effort to hunt for more efficient and sustainable energy. Hydrogen, an alternative energy source, can be produced by photocatalytic water splitting with semiconductors as catalysts, which was discovered by Honda and Fujishima in 1972 [3,4]. In recent decades, research on the decomposition of water by photocatalyst has achieved certain achievements [[5], [6], [7]]. But the great challenge of this hydrogen-production method is that photogenerated electron-hole pairs are easily recombined, so that the quantum conversion efficiency is low. Therefore, finding an effective photocatalyst with low electron-hole pairs recombination rate and thus the better performance in photocatalytic reaction remains a goal in the research area of water splitting into H2.

Graphite carbon nitride (g-C3N4) has been viewed as an attractive candidate for photocatalytic HER (hydrogen evolution reaction) by virtue of its fascinating properties, such as photochemical durability, proper band position and earth-abundance [8,9]. In spite of these advantages as a photocatalyst, it also has some disadvantages, like low photogenerated electron-hole separation rate and limited visible light utilization efficiency. In recent years, research focused on graphite carbon nitride has been widely carried out [[10], [11], [12], [13], [14]]. In order to overcome these shortcomings, different modification strategies are employed, one of which is elemental doping. So far, non-metallic elements (C [15,16], N [17], O [18], P [19], S [20,21], Br [22], I [23], B [24,25], P–S co-doped [26], S–B co-doped [27], B–P co-doped [28] et al.) and metallic elements (Fe [29], Co [30], Cu [31], Zn [32] et al.) were doped into graphite carbon nitride via high temperature thermal polymerization. Among them, N-doped g-C3N4 (NCN) has shown superior light absorption ability and charge transfer efficiency compared to pristine g-C3N4 under visible light conditions. Therefore, NCN has a good prospect as an excellent photocatalyst for producing hydrogen through water splitting under visible light.

Presently, noble metal (eg., Pt [33], Ru [34] and Ag [35]) plays a crucial role in photocatalytic water splitting reaction as a cocatalyst. Depositing platinum on the surface of graphite carbon nitride can efficiently accelerate the electron transfer and improve the HER efficiency. However, the high price of precious metal can not meet the needs of industrial hydrogen production. Therefore, it is necessary to find a low-cost co-catalyst to replace noble metal platinum and enhance the photocatalytic performance. Nickel is a non-noble-metal, and nickel-based compounds like NiS [36], NiS2 [37,38], Ni2P [39], Ni12P5 [40], Ni2P2O7 [41], NiCo2O4 [42], Ni(OH)2 [43] et al. have exhibited good catalytic performance in visible-light driven water splitting process. From this point of view, it was proposed that zero-valent nickel may act as a co-catalyst to enhance the performance of photocatalytic HER reaction.

In this manuscript, an efficient hydrogen production photocatalyst, NiNCN3, was reported which was prepared by the photodeposition of nickel metal nanoparticles on NCN nanosheets. The photocatalytic activity of NiNCN3 under visible light is 1507 μmol g−1 h−1, which is higher than the catalytic activity of 3 wt% Pt/NCN (1055 μmol g−1 h−1). Moreover, a photocatalytic HER mechanism of NiNCN is also discussed.

Section snippets

Chemical reagent

All reagents were of analytical grade and not further purified. Nickel nitrate hexahydrate, sodium hypophosphite monohydrate and citric acid monohydrate were purchased from Sinopharm Chemical Reagent Co., Ltd. Urea was obtained from Shanghai Lingfeng Chemical Reagent Co., Ltd. Triethanolamine was purchased from Aladdin.

Preparation of N-doped g-C3N4

N-doped g-C3N4 was produced by typical high-temperature thermal polymerization [17]. 5 g urea was mixed with 5 mg citric acid monohydrate, and subsequently the mixture was placed

Characterization of photocatalyst

XRD is used to investigate the phase structure of the sample. Fig. 1a shows the XRD patterns of CN, NCN and NiNCN. Two diffraction peaks were observed at 13.3° and 27.5°, which belong to the (100) and (002) crystal plane of CN, respectively. The weak peak at 13.3° is due to the in-plane structural modes of CN and the strong peaks at 27.5° can be indexed as the (002) plane which is from the interlayer stacking of π-conjugated aromatic systems (JCPDS #87-1526). For NCN and NiNCN, strong

Conclusions

In summary, NiNCN3, a photocatalyst with Ni nanoparticles loaded on N-doped graphite carbon nitride, was successfully prepared by photodeposition. NiNCN3 exhibits excellent photocatalytic performance with a hydrogen evolution rate of 1507 μmol g−1 h−1. The excellent light absorption and efficient electron transfer of the photocatalyst lead to the outstanding photocatalytic performance. Since all the elements presented in the photocatalyst are non-precious, our research creates a good prospect

Acknowledgements

This work was supported by State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences (20170028); State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University, KF1823; Shanghai Pujiang Program (15PJ1400200).

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