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Dye-sensitized solar cells (DSSCs) have attracted widespread attention in recent years as potential cost-effective alternatives to silicon-based and thin-film solar cells. Within typical DSSCs, the counter electrode (CE) is vital to collect electrons from the external circuit and catalyze the I3- reduction in the electrolyte. Careful design of the CEs can improve the catalytic activity and chemical stability associated with the liquid redox electrolyte used in most cells. In this Progress Report, advances made by our groups in the development of CEs for DSSCs are reviewed, highlighting important contributions that promise low-cost, efficient, and robust DSSC systems. Specifically, we focus on the design of novel Pt-free CE catalytic materials, including design ideas, fabrication approaches, characterization techniques, first-principle density functional theory (DFT) calculations, ab-initio Car-Parrinello molecular dynamics (CPMD) simulations, and stability evaluations, that serve as practical alternatives to conventional noble metal Pt electrodes. We stress the merits and demerits of well-designed Pt-free CEs, such as carbon materials, conductive polymers, transition metal compounds (TMCs) and their corresponding hybrids. Also, the prospects and challenges of alternative Pt catalysts for their applications in new-type DSSCs and other catalytic fields are discussed., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Though perovskite solar cells (PSCs) or modules (PSMs) are being developed at an unprecedented speed, several obstacles remain to their commercialization. One of the difficult problems is the expensive and unstable Au and Ag counter electrode. Therefore, highly effective, stable, and low‐cost counter electrode materials should be explored. Among various counter electrode materials, carbon is one of the most promising substitutes for their rich sources, low cost, outstanding electrochemical performance, and diversified surface functions. This review summarizes recent achievements of carbon counter electrode materials, which included commercial carbon paste, carbon black, graphite, graphene, carbon nanotubes and their synthetic approaches, modifications, and structure‐function relationships. Moreover, large‐scale carbon counter electrode in PSCs or PSMs are specifically discussed. Hopefully, this recapitulative analysis will draw the attention of relevant researchers to re‐understand the importance of counter electrode and clarify what should be noticed to develop qualified counter electrode materials for PSCs or PSMs. [ABSTRACT FROM AUTHOR]

Recently, sodium‐ion batteries have attracted great attention, owing to the rich resource and low cost. In the present work, a feather‐like MnO2 nanostructure was prepared directly on carbon paper by using a rapid and simple hydrothermal route for the first time. The formation mechanism was proposed by investigating the intermediate products during the reaction. When applied as an anode for a sodium‐ion battery, the feather‐like MnO2 nanostructure on carbon paper exhibited a high discharge capacity, good rate reversibility, and long‐term cycling stability. A high specific capacity of approximately 300 mAh g−1 could be obtained even after cycling 400 times with a current density of 0.1 A g−1. Furthermore, the Na+ storage mechanism of MnO2 on carbon paper in the sodium‐ion battery was also investigated in this work. Such high performance can be attributed to the porous structure of the substrate and high specific surface area of the feather‐like nanostructure. Caps off: The feather‐like MnO2 nanostructure is grown in situ on carbon paper and delivers a high performance as an anode for sodium‐ion batteries. [ABSTRACT FROM AUTHOR]

Dye-sensitized solar cells with sub-5 μm-thick Pt/SiC-P (1.79 at. % Pt), Pt/SiC-M (0.45 at. % Pt), and Pt/SiC-R (0.39 at. % Pt) counter electrode (CE) films fabricated by using three different processes produced power conversion efficiencies of 6.82, 7.64, and 7.04 % that reached 86.5, 97.0, and 89.3 %, respectively, of the level obtained by using a print-Pt CE (7.88 %). These materials can reduce the cost of CEs and solve challenges involving Pt. [ABSTRACT FROM AUTHOR]

Mesoporous-graphitic-carbon-supported HfO2 (HfO2-MGC) nanohybrids were synthesized by using a soft-template route. Characterization and a systematic investigation of the catalytic properties, stability, and catalytic mechanism were performed for HfO2-MGC counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The new HfO2-MGC as a CE in DSSCs showed a surprisingly high efficiency of 7.75 % for the triiodide/iodide redox couple and 3.69 % for the disulfide/thiolate redox couple, greater than the Pt electrode in the corresponding electrolyte system, which opens up a possibility for its practical application. [ABSTRACT FROM AUTHOR]

Titanium carbide (TiC) has been used as a counter electrode (CE) catalyst in place of Pt for triiodide reduction in dye-sensitized solar cells (DSCs). Its catalytic activity can be comparable to that of Pt. The effect of the thickness of the TiC layer on the performance of the DSCs was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and Tafel polarization measurements. We found that as the film thickness increased, the fill factor and short-circuit current density increased, which led to improved power-conversion efficiency. When the TiC film was thicker than 20 μm, however, no significant continuous improvement in the catalytic activity was observed. A high power-conversion efficiency of 6.46 % was obtained for the DSC by using a TiC CE at the optimized film thickness, a value similar to that obtained with a Pt CE. [ABSTRACT FROM AUTHOR]

Abstract: Several types of counter electrodes based on flexible metal and plastic substrates for dye-sensitized solar cells (DSCs) have been investigated. The DSCs composed of the counter electrodes based on a stainless steel substrate, a nickel sheet and a conducting plastic film, have obtained conversion efficiencies comparable to that based on the conducting glass. The counter electrode based on the stainless steel substrate has the merit of improving the fill factor and conversion efficiency of the DSC by reducing its internal resistance. The counter electrode based on a polyester film can be aimed at lower cost markets. These counter electrodes based on the metal and plastic substrates are applicable for flexible DSCs. [Copyright &y& Elsevier]

A composite catalyst of rosin carbon/Fe3O4 with marvellous morphology was synthesized and applied as a counter electrode (CE) in dye-sensitized solar cells (DSCs), demonstrating notable electrocatalytic activity for the reduction of I3−. Based on this CE, a high power conversion efficiency of 8.11% was achieved, comparable to that of the traditional Pt CE. [ABSTRACT FROM AUTHOR]

Porous chalcogels CoMoS4 and NiMoS4 made by a facile solution reaction displayed good electrocatalytic activity in the redox reaction of the I−/I3− 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%). [ABSTRACT FROM AUTHOR]

For the first time, nonstoichiometric WO2.72 was used as a counter electrode (CE) in dye-sensitized solar cells (DSSCs). Oxygen-vacancy-rich WO2.72 nanorod bundles with notable catalytic activity for triiodide and thiolate reduction were prepared in this study. The photovoltaic parameters of dye-sensitized solar cells (DSSCs) with WO2.72 nanorod bundles as CEs are superior compared with those of the WO3-based cells, and nearly the same as those of the precious metal Pt-based cells. In a non-corrosive organic redox couple, the performance of WO2.72 CEs is better than that of Pt and WO3 CEs in DSSCs. [ABSTRACT FROM AUTHOR]

Synthesized niobium oxides (Nb2O5and NbO2) were applied for the first time as counter electrodes (CEs) in dye-sensitized solar cells (DSCs). The DSC using NbO2CE showed a higher power conversion efficiency of 7.88%, compared with that of the DSC using Pt CE (7.65%). [ABSTRACT FROM AUTHOR]

Tungsten dioxide (WO2) nanorods were synthesized, which showed excellent catalytic activity for the reduction of triiodide to iodide. The dye-sensitized solar cell (DSC) using WO2as a counter electrode (CE) reached a high energy conversion efficiency of 7.25%, which can match the performance of the DSC based on a Pt CE. [ABSTRACT FROM AUTHOR]

One of the major problems limits the applications of perovskite solar cells (PSCs) is the high cost of hole transporting materials (HTMs) and noble metallic electrodes. For HTMs and noble-metal-free PSCs, carbon materials have been utilized as counter electrodes (CEs). In this paper, four kinds of ultra-low-cost bio-carbon materials have been applied and compared in PSCs. Results showed that the photovoltaic performance of PSCs based on different bio-carbon CEs was determined by the interfacial connection, work function (WF), sheet resistance, crystallinity, and morphology of these bio-carbons. The high PCE (12.82%) of PSCs based on bio-carbon CEs has been achieved in current state-of-the-art. PSCs based on bio-carbon CEs was more stable than that of conventional devices, which could retain 87% of their initial PCE after storing for 2000 h in room temperature. Our work proposes a new pathway for the exploration of low-cost bio-carbon materials and could accelerate the applications of PSCs based on carbon electrode. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Two-dimensional (2D) VS 2 nanosheets along the NiCo 2 S 4 needle arrays were prepared via an in situ sulfurization-assisted hydrothermal process. The unique nanostructure and phase were characterized by using field effect scanning electron microscope (FESEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction. The electrochemical properties were recorded by cyclic voltammetry, charge/discharge curves, and electrochemical impedance spectroscopy. The binder-free NiCo 2 S 4 @VS 2 electrode has contributed to a high specific capacity of 1023. 4 C g−1 with remarkable stability where 96% of its capacity retained after 2000 cycles at the current density of 0.45 A g−1 due to the synergetic effects. Promoting for practical applications, an asymmetric supercapacitor (ASC) composed of NiCo 2 S 4 @VS 2 as the positive electrode and activated carbon (AC) as the negative electrode with polypropylene as the separator was fabricated. The assembled ASC contributed to a maximum energy density of 31.2 Wh kg−1 at the power density of 775 W kg−1 with good stabilities under different current densities. Thereby, this rational design provides a new strategy for synthesizing electrode materials for high-performance supercapacitors. Graphical abstract Image 1 Highlights • The NiCo 2 S 4 @VS 2 was firstly grown on Ni foam by two-step hydrothermal method. • A maximum energy density of 31.2 Wh kg−1 at the power density of 775 W kg−1. • Good cycle stabilities under different current densities. [ABSTRACT FROM AUTHOR]

Review: [96 refs. [ABSTRACT FROM AUTHOR]

Pt/carbon fiber composite (Pt/Cf) with a low Pt loading of 1.0 wt% is introduced into dye-sensitized solar cells as counter electrode (CE) catalyst. The cobalt-electrolyte based device using this composite CE achieves power conversion efficiency of 8.97%, a great improvement of 40.4% as compared to the Cf CE based device. This research provides a feasible route to reduce the dosage of Pt in DSCs system, benefiting for the commercial application of DSCs. [ABSTRACT FROM AUTHOR]

Abstract: Binary composite of Pt decorated transition metal compounds (WO2, TiC, and VN) were introduced into dye-sensitized solar cells and excellent performance were obtained, almost 20% better than unitary materials. Ternary composite of Pt/WO2/TiO2 was also prepared to further improve the photovoltaic performance. [Copyright &y& Elsevier]

Abstract: The Pt-like electrocatalytic activity of counter electrodes (CEs) prepared from tantalum oxides for dye-sensitized solar cells (DSCs) is demonstrated. The low ratio of oxygen to metal atom of the oxide favors the electrocatalytic activity of these CE materials for I3 − reduction in DSCs. TaO, used as a CE in DSCs, shows superior electrocatalytic activity and a high power conversion efficiency of 6.48%, up to 90.5% of the level obtained using Pt as a CE (7.16%). This work develops the use of novel tantalum oxide CE materials for low cost and high efficiency DSCs. [Copyright &y& Elsevier]

Abstract: Three different types of nanocrystalline, N-doped TiO2 electrodes were synthesized using several nitrogen dopants through wet methods. The obtained nanocrystalline, N-doped TiO2 electrodes possessed different crystallite sizes, surface areas, and N-doping amounts. Characterizations were performed to reveal the nitrogen-doping processes for the wet methods using ammonia, urea, and triethylamine as the nitrogen dopants. Additionally, a high conversion efficiency of 8.32% was achieved by the dye-sensitized solar cells, based on the N-doped TiO2 electrodes. For instance, in comparison with the commercial P25 (5.76%) and pure anatase TiO2 electrodes (7.14%), significant improvements (44% and 17%, respectively) in the efficiencies were obtained. The findings also indicated that the ammonia nitrogen dopant was more efficient than other two nitrogen dopants. The electron transports, electron lifetimes, and charge recombination in the dye-sensitized N-doped TiO2 solar cells also differed from those in the pure TiO2-based dye-sensitized solar cells (DSCs). Specifically, an enhanced photocurrent of ca. 36% in N-doped DSCs resulted from the synergistic effects of the high dye uptake and the efficient electron transport. Moreover, the relationship between charge and voltage revealed that less charge was needed to get a high open-circuit voltage in the N-doping films. [Copyright &y& Elsevier]