A branching NiCuPt alloy counter electrode for high-efficiency dye-sensitized solar cell

doi:10.1016/j.apsusc.2015.11.216

Applied Surface Science

Volume 362, 30 January 2016, Pages 28-34

https://doi.org/10.1016/j.apsusc.2015.11.216 Get rights and content

Highlights

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A branching NiCuPt alloy CE is synthesized for DSSC applications.
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The catalytic activity is markedly enhanced by optimizing synthesis conditions.
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The dissolution resistance of NiCuPt alloy CE is enhanced.
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The DSSC with NiCuPt yields an optimal efficiency of 9.66%.

Abstract

A rising objective for high-efficiency dye-sensitized solar cells (DSSCs) is to create extraordinary and cost-effective counter electrode (CE) electrocatalysts. We present here a branching NiCuPt alloy CE synthesized by electrodepositing Ni on ZnO microrod templates and subsequently growing branched Cu as well as suffering from a galvanic displacement for Pt uptake. The resultant NiCuPt alloy CE displays a promising electrocatalytic activity toward redox electrolyte having I⁻/I₃⁻ couples. An impressive power conversion efficiency of 9.66% is yielded for the liquid-junction DSSC platform.

Graphical abstract

Introduction

Dye-sensitized solar cell (DSSC) is an electrochemical device converting solar energy into electricity by complicated photoelectrochemical reactions [1], [2], [3]. Although DSSC has experienced more than 20 years [4], there still are many unsolved problems including high cost of preferred Pt counter electrode (CE) [5], limited light absorption [6], and electrolyte leakage [7]. To address these issues, many efforts have been made to replace Pt CE by carbonaceous materials [8], conductive polymers [9], compounds [10], and Pt-free alloy [11] or at least to reduce Pt dosage. Among various low-Pt CE candidates, Pt alloys have established themselves as promising electrocatalysts in collecting electrons and catalyzing I⁻/I₃⁻ redox couples in liquid electrolyte. In our previous works, we have successfully alloyed Pt with transition metals such as Co [12], Ni [13], Ru [14], and Mo [15]. In comparison with pristine Pt, the electrocatalytic activities of Pt alloy CEs have been significantly enhanced due to the redistributed electronic structure and matching work functions to redox potential of I⁻/I₃⁻ electrolyte.

In searching for other robust Pt alloy CEs, we present here the fabrication of branching NiCuPt ternary alloy using aligned ZnO nanorods as templates. After electrodeposition of Ni and Cu, and galvanic displacement of Ni/Cu by H₂PtCl₆, the resultant NiCuPt displays branched structure having Ni backbone and Cu branches. An efficiency of 9.66% is determined on the liquid-junction DSSC by tuning the displacement time of H₂PtCl₆ species.

Section snippets

Growth of aligned ZnO microrods

The aligned ZnO microrods were synthesized using a common hydrothermal process. In details, 2.975 g of Zinc nitrate hexahydrate [Zn(NO₃)₂·6H₂O, 99%] and 1.402 g of hexamethylenetetramine (HTMA, C₆H₁₂N₄, 99%) were mixed in 100 mL deionized water. Subsequently, the freshly cleaned FTO glass substrates (12 Ω square⁻¹) were put face up in the above solution at 95 °C for 12 h. After cooling to the room temperature, the ZnO microrods were thoroughly rinsed by deionized water, dried in the air, and calcined

Results and discussion

Fig. 1a shows the top-view of aligned ZnO microrodes, yielding hexagonal ZnO microrods with an average diameter of ∼1.5 μm. Due to the semiconductor nature of ZnO microrods, the metallic Ni can be electrodeposited onto ZnO microrods. The ZnO can be removed in H₂SO₄ aqueous solution, allowing for the formation of Ni microtubes (Fig. 1b). Due to the much lower reduction potentials of Ni²⁺/Ni (−0.23 V vs. SHE) and Cu²⁺/Cu (+0.34 V vs. SHE) than PtCl₆²⁻/Pt (+0.735 V vs. SHE), the superficial Ni and Cu

Conclusions

In summary, a branching NiCuPt alloy CE has been successfully designed by combining Ni backbones with branched Cu, followed by galvanic displacement of outward Ni and Cu by H₂PtCl₆. The resultant NiCuPt alloy CE displays superior electrocatalytic activity and charge-transfer ability, arising from good matching of work function to redox potential of liquid electrolyte. Due to the competitive dissolution reactions between Ni or Cu and I₂/I₃⁻ species, the persistent stability of NiCuPt alloy CE is

Acknowledgement

The authors would like to acknowledge financial supports from National Natural Science Foundation of China (21503202, U1037604).

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A branching NiCuPt alloy counter electrode for high-efficiency dye-sensitized solar cell

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Growth of aligned ZnO microrods

Results and discussion

Conclusions

Acknowledgement

Electrochim. Acta

Appl. Surf. Sci.

Appl. Surf. Sci.

Appl. Surf. Sci.

Electrochim. Acta

J. Power Sources

Electrochim. Acta

Electrochim. Acta

Sol. Energy Mater. Sol. C

Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of polyphyrin sensitizers

Nat. Chem.

Highly efficient photocathodes for dye-sensitized tandem solar cells

Nat. Mater.