VC@C composites derived from polyoxovanadate assisted by dicyandiamide as low-cost platinum-free counter electrode electrocatalyst for dye-sensitized solar cells

Vanadium-based carbides have been applied as Pt-free counter electrodes (CEs) electro-catalysts for dye-sensitized solar cells (DSSCs) due to the advantages of earth-abundant reserves, diverse composition, ease modification, and low cost. Herein, the polyoxovanadate (NH₄)₂V₆O₁₆ as V source assisted by dicyandiamide (C₂H₄N₄) as C source via simply physical mixing by ball-milling to assemble VC@C precursors. And then, five different VC@C composites derived from precursors with mass ratios of dicyandiamide to polyoxovanadate of 5:1, 10:1, 15:1, 20:1 and 25:1 at 900 °C, and further achieved power conversion efficiencies (PCEs) of 5.4%, 5.6%, 6.6%, 6.2% and 5.1% as CEs for regenerate traditional I₃⁻/I⁻ couple in the encapsulated DSSCs, respectively. The effects of different mass ratio of dicyandiamide on the catalytic performances of VC@C composite CEs were also assessed using cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization experiments. The photocurrent-photovoltage (J-V) results indicated that VC@C composites CEs had high conductivity and rich number of active sites, which indicated that VC@C composites could be a cost-effective and high-performance alternative Pt-based CEs catalyst for DSSCs.     

CoxMo(1−x)S2 intermixed reduced graphene oxide as efficient counter electrode materials for high-performance dye-sensitized solar cells

In this study, nanocomposite electrocatalysts composed of cobalt molybdenum sulfide flower-like nanosheets intermixed with reduced graphene oxide (Co_xMo_(1?x)S₂/rGO) were prepared by a facile one-step hydrothermal method and were used to prepare counter electrodes (CE) of high-performance dye-sensitized solar cells (DSSCs). The structural and morphological analysis of the nanocomposites were carried out using field emission scanning electron microscopy, micro-Raman, and X-ray photoelectron spectroscopies, which revealed 2-dimensional petal-like nanosheets of the ternary metal sulfides intermixed with the reduced graphene oxide sheets. The DSSCs fabricated using Co_xMo_(1?x)S₂/rGO (CMS-2/rGO) as the counter electrode material exhibited power conversion efficiency (PCE) of 9.04%, which was found to be superior to the PCEs of DSSCs with CEs made of MoS₂/rGO (7.56%), Co_xMo_(1-x)S₂ (7.04–7.78%), and conventional Pt (8.72%). The electrochemical measurements showed that the excellent electrocatalytic activity of the Co_xMo_(1?x)S₂/rGO on I₃^- can be attributed to the expanded active sites, improved charge transfer across the CE, and reduced electrode/electrolyte interface resistance. The facile preparation approach and outstanding catalytic behavior of Co_xMo_(1?x)S₂/rGO indicate that the nanostructured Co_xMo_(1-x)S₂/rGO intermix would be a cost-effective material over the platinum used in the CE of DSSCs.     

Comparative study on the electrochemical performance of coals and coal chars in a molten carbonate direct carbon fuel cell with a novel anode structure

Molten carbonate direct carbon fuel cells (MC-DCFCs) allow the efficient and clean use of coal. In this study, a novel anode structure is designed, and the performances of six coal-based fuels are investigated in MC-DCFC. The mechanisms of performance differences are investigated, as well as the effect of operating temperature on performance. The results reveal the fuel cell performance in the following order: meagre coal (109.8) ≈ bituminous coal (108.7) > bituminous coal char (98.1) > lignite coal (83.7) > lignite coal char (71.3) > meagre coal char (53.2) in mW cm^?2. Coal performs better because of its high carbon content, high volatile content, rich oxygen-containing functional groups, larger specific surface area, stronger thermal reactivity, and other factors. The electrochemical reactivity of coal fuel increased with higher reaction temperatures and varied throughout the temperature ranges. This study implies that using coal fuel to commercialize MC-DCFC could be a realistic alternative.