Design of plasmonic CuCo bimetal as a nonsemiconductor photocatalyst for synchronized hydrogen evolution and storage

https://doi.org/10.1016/j.apcatb.2018.10.020Get rights and content

Highlights

  • CuCo bimetal were prepared by hydrothermal method.

  • Photocatalytic water splitting was enhanced after modification with Co nanosheets.

  • The integration of hydrogen evolution and storage was realized in this device.

  • A possible mechanism is elucidated for the photocatalytic activity improvement.

Abstract

Solar-driven hydrogen evolution with sustainable energy sources, which require earth-abundant, robust and efficient photocatalysts for fuel production, is highly desirable. Here, we propose an alternative promising configuration of a dendrite-like plasmonic CuCo bimetal as a nonsemiconductor photocatalyst, which exhibits exceptional photocatalytic activities for H2 evolution (77.1 μmol g−1 h−1) under sunlight irradiation without a sacrificial agent. Notably, a certain amount of hydrogen evolved by photocatalytic water splitting was conserved by the photocatalyst at room temperature, demonstrating that the integration of hydrogen evolution and storage was realized in this device. Electrons were produced by the surface plasmon resonance (SPR) effect of the Cu component in CuCo bimetal, and Co nanosheets were grown in situ on the surface of Cu, which can facilitate the transfer of photoinduced charge as a cocatalyst. Specifically, the photocatalyst shows excellent chemical stability with X-ray photoelectron spectroscopy and X-ray diffraction characterization after four consecutive cycles over a total of 20 h. This work provides insights into a plasmonic nonsemiconductor photocatalytic system in the hydrogen energy field.

Introduction

Recently, plasmonic photocatalysts with a fascinating surface plasmon resonance (SPR) effect have attracted tremendous attention in the field of efficient conversation of solar energy to chemical energy because they can harvest and utilize low-energy photons from sunlight even in the near-infrared region [[1], [2], [3], [4], [5]]. With resonant photon excitation in the incident light, collective oscillations of free charge carriers will occur on the surface of plasmonic photocatalysts and the oscillation electrons can participate in photocatalytic reactions [[6], [7], [8], [9]]. In this regard, one successful paradigm is the introduction of plasmonic noble-metal as a co-catalyst into the photocatalytic system by promoting charge separation and transfer, such as with Au and Ag [[10], [11], [12]]. However, Au and Ag are only cocatalysts and the core of the photocatalytic system is still a semiconductor. Moreover, these noble-metals are expensive and not beneficial for large-scale applications. Plasmonic Cu as a photocatalyst has drawn considerable interest due to its SPR effect, high conductivity, low cost and promising photocatalytic activity, and its photocatalytic properties have been investigated [13,14]. Therefore, Cu is a promising candidate in the photocatalytic field as a nonsemiconductor photocatalyst, which could greatly broaden the scope of the photocatalytic system.

Alloying with other metals to form bimetal is an effective method to change the intrinsic activity of the Cu activity sites. The electron transfer process can be tuned, and the recombination drawback of electron-hole pair can be suppressed due to strain and ligand effects after alloying [15,16]. Cobalt (Co), is a stable, abundant and low-cost metal in the earth and, has broad-spectrum absorption properties and excellent charge transfer abilities [17,18]. More importantly, the hydrogen storage capacity of Co has been reported and this special property can realize the integration of hydrogen evolution and storage [17]. Hence, plasmonic Cu couples with Co to form a bimetal, potentially enabling highly efficient photocatalytic H2 evolution and storage. CuCo bimetal has been applied in many fields such as hydrolytic dehydrogenation of ammonia borane [19], higher alcohol synthesis from syngas [20,21] and syngas conversion [22]. However, to date, the photocatalytic application of plasmonic CuCo bimetal has not been reported.

In this study, a plasmonic CuCo bimetal photocatalyst is rationally designed and prepared using hydrothermal growth. The orientation growth of Co nanosheets grown on the surface of dendrite-like Cu was obtained, and the bimetal activity of the photocatalytic overall water splitting was investigated. Furthermore, the bimetal photocatalyst shows an interesting hydrogen storage response. Two major challenges of hydrogen evolution and storage can be solved simultaneous. This material is a choice for bimetal components because dendrite-like Cu shows an SPR effect for the production of photoinduced electrons, and its work function is lower than that of Co, leading to charge transfer from Cu to Co under a general excitation. Through transient photocurrent responses and steady-state photoluminescence spectra, we demonstrate that SPR excitation of CuCo bimetal can induce the transfer of plasmonic electron from Cu to Co, boosting the production of photoinduced electrons for executing the photocatalytic reaction. In this way, CuCo bimetal prepared with an optimal temperature and ratio exhibits enhanced photocatalytic activity compared with pure dendrite-like Cu under sunlight irradiation.

Section snippets

Materials

All reagents are analytical grade and used without further purification and deionized water was used in all experiments. Cobalt chloride hexahydrate (CoCl2·6H2O) (AR), copper chloride dihydrate (CuCl2·2H2O) (AR), lactic acid (97%) ethylenediamine (AR), sodium hypophosphite (AR), sodium hydrate (NaOH) and absolute ethanol were purchased from Sinopharm Chemical Reagent Co. Ltd., P.R. China.

Synthesis of CuCo bimetal

CuCo bimetal was prepared using the hydrothermal method described below. In a typical synthesis, x mmol of

Formation and characterization

XRD patterns were used to analyze the crystallization degree and crystal structure of the samples. As shown in Fig. 1a, one can see two different crystalline phases, which are attributed to the cobalt phase (JCPDS NO. 89-4308) [23] and copper phase (JCPDS NO. 04-0836) [24]. The cobalt phase was not formed at 140 °C and only the copper phase was generated due to different standard reduction potentials of Cu and Co [25]. When the temperature was above 140 °C, an apparent cobalt phase appeared in

Conclusions

In summary, dendrite-like plasmonic Cu with photocatalytic activity for H2 evolution was successfully prepared. The collected SPR frequency photons are exclusively transferred to charge carriers via the SPR effect to participate in photocatalytic water splitting. Intriguingly, its photocatalysis could be greatly enhanced after modification with Co nanosheets, especially with an optimal ratio, and even with a respective ≈ 3.5-fold time improvement for H2 evolution compared to the Cu itself.

Acknowledgements

We thank the National Natural Science Foundation of China (No. 21571064, 21371060), the PhDStart-up Fund of Natural Science Foundation of Guangdong Province, the Fundamental Research Funds for the Central Universities and the research fund of the Key Laboratory of Fuel Cell Technology of Guangdong Province for financial support.

References (54)

  • P. Zhang et al.

    Appl. Catal. B: Environ.

    (2018)
  • Y. Zhang et al.

    J. Catal.

    (2017)
  • Y. Zhang et al.

    J. Catal.

    (2018)
  • P. Zhang et al.

    Appl. Catal. B: Environ.

    (2017)
  • A. Yousef et al.

    Electrochim. Acta

    (2013)
  • Y. Liu et al.

    Appl. Surf. Sci.

    (2018)
  • G. Liu et al.

    Appl. Catal., A

    (2014)
  • L. Chiang et al.

    J. Hazard. Mater.

    (2014)
  • P. Zhang et al.

    Appl. Surf. Sci.

    (2017)
  • X. Chen et al.

    Chem. Eng. J.

    (2017)
  • A. Bulut et al.

    Appl. Catal. B

    (2016)
  • Y. Liu et al.

    Appl. Surf. Sci.

    (2018)
  • H.B. Dai et al.

    Catal. Today

    (2011)
  • T. Song et al.

    Appl. Catal., B

    (2018)
  • Y. Zhang et al.

    Appl. Catal., B

    (2019)
  • Y. Li et al.

    Int. J. Hydrogen Energy

    (2011)
  • H. Petek et al.

    Prog. Surf. Sci.

    (1997)
  • N. Zhang et al.

    Nat. Photonics

    (2016)
  • S. Linic et al.

    Nat. Mater.

    (2011)
  • A. Giugni et al.

    Nat. Nanotechnol.

    (2013)
  • G.V. Hartland

    Chem. Rev.

    (2011)
  • J. Olson et al.

    Chem. Soc. Rev.

    (2015)
  • D.Y. Wan

    Nat. Commun.

    (2017)
  • Y. Shi et al.

    J. Am. Chem. Soc.

    (2015)
  • G. Liu et al.

    J. Am. Chem. Soc.

    (2016)
  • Y. Kang et al.

    Nanoscale

    (2015)
  • J. Li et al.

    Nat. Photonics

    (2015)
  • Cited by (0)

    View full text