Low-cost and high-performance CoMoS4 and NiMoS4 counter electrodes for dye-sensitized solar cells

Abstract

Porous chalcogels CoMoS 4 and NiMoS 4 made by a facile solution reaction displayed good electrocatalytic activity in the redox reaction of the I À /I 3 À shuttle. Dye-sensitized solar cells with these ternary compounds as counter electrodes (CEs) showed photovoltaic performance similar to the devices made with noble metal platinum CE (7.46%).Dye-sensitized solar cells (DSSCs) have attracted significant attention as low-cost alternatives to traditional photovoltaic devices. 1,2 In DSSCs, counter electrodes (CEs) with both excellent electrocatalytic activity and high electrical conductivity are indispensable to obtain a low overvoltage and to accelerate the regeneration of I À from I 3 À . Due to the fact that noble metal Pt, the most widely used material for CEs at present, is very expensive, studies have recently been made extensively on low-cost Pt-like alternatives, including carbonbased materials, 3 conducting polymers, 4 and metals in the form of oxides, 5 sulfides, 6-10 selenides, 11 nitrides, 12 and carbides, 13 and great promise has been demonstrated in this field. Extension of the CE materials to ternary compounds may greatly expand this research platform. Catalysts based on molybdenum or tungsten sulfides have been widely used for hydrodesulfurization and hydrogen evolution reaction by electrocatalysis, and introduction of Co or Ni promoters into these matrices results in significant enhancement in the catalytic activities. 14-16 Kanatzidis et al. 17 have most recently reported the synthesis of porous CoMoS 4 and NiMoS 4 via facile solution reactions. In this work, we have applied these ternary materials with and without graphite additives as the counter electrodes in DSSCs. The resulting photovoltaic devices showed power conversion efficiency up to 7.31%, comparable to the DSSCs made with an expensive platinum-based counter electrode (7.46%).Ammonium tetrathiomolybdate (NH 4 ) 2 MoS 4 was obtained by the reaction of (NH 4 ) 6 Mo 7 O 24 Á4H 2 O and (NH 4 ) 2 S aqueous solution at ambient temperature. CoMoS 4 and NiMoS 4 were synthesized as previously described. 17 Briefly, Co(NO 3 ) 2 Á6H 2 O, Ni(NO 3 ) 2 Á6H 2 O and (NH 4 ) 2 MoS 4 were dissolved in formamide separately, and then Co or Ni precursor solution was added into the tetrathiomolybdate solution. In these reactions, cationic species of VIII group metals interacted with thiomolybdate anions, leading to precipitation of solids. As the polymerization proceeded, the viscosity of the solution increased, which eventually solidified to a monolithic black gel. It took 7-14 days for the viscous solution to transform into a rigid gel. The products were then annealed at 300 1C in a nitrogen atmosphere and characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), scanning and high-resolution transmission electron microscopy (HRTEM).Both Ni-and Co-based chalcogels were found to be amorphous, as indicated by the predominant broad features in the XRD patterns (Fig. S1, ESI †). A similar resu...

Design a novel kind of open-ended carbon sphere for a highly effective counter electrode catalyst in dye-sensitized solar cells

“…Unlike the semiconductor, dye, and redox shuttle components, counter electrode (CE) catalysts are often overlooked. Fortunately, CE catalysts begun to attract increasing attention, as a class of new CE catalysts, such as carbon materials, [9][10][11][12] organic polymers, [13][14][15][16] and metal compounds [17][18][19][20][21][22][23][24][25][26][27][28][29][30] have been applied to replace conventional noble Pt CE. Among these Pt-free materials, carbon is a promising CE catalyst for use in DSCs because of its low cost, high conductivity, high catalytic activity, ready availability, high thermal stability, and corrosion resistance.…”

Amorphous nickel/cobalt tungsten sulfide electrocatalysts for high-efficiency hydrogen evolution reaction

“…Owing to the smaller electron density on the S atoms, the proton affinity of WS 4 2− is lower than that of MoS 4 2− [48]. The MS 4 2− ion with lowlying unoccupied orbitals shows versatile coordination behavior with Ni 2+ or Co 2+ forming complexes like [M (MS 4 ) 2 ] n− or M MS 4 [49][50][51][52]. In these complexes, the strong 3d-interactions in the ligand orbitals (i.e.…”

“…The Ni 2+ or Co 2+ cations can interact with tetrathiomolybdate or tetrathiotungstate anions (MS 4 2− ) to form complexes like [M'(MS 4 ) 2 ] n− or M MS 4 (M = Ni, Co; M = Mo, W; n = 2, 3) which exhibit strong M → MS 4 electron delocalization [48][49][50][51][52]. Hence, Ni/Co incorporation and thermal treatment can be implemented together to optimize the amorphous structure.…”

WB crystals with oxidized surface as counter electrode in dye-sensitized solar cells

“…The excellent performance of Pt based counter electrode is attributed to both the high catalytic activity of Pt in inducing triiodide reduction reaction and its high electrical conductivity [8], which enable fast electron transfer from the counter electrode to electrolyte in the cell. In the past years, various earth-abundant materials including carbon [13][14][15][16], transition metal sulphides [17][18][19], carbides [20,21], nitrides [22,23], phosphides [24,25] and oxides [26][27][28][29][30][31][32][33][34][35] have been explored and shown a great potential as counter electrode materials. It is anticipated that the continuous extension of the database of Pt-free counter electrode materials will make it possible to develop low-cost high-efficiency DSSCs for large-scale applications.…”