Atomic Rearrangement in Core–Shell Catalysts Induced by Electrochemical Activation for Favorable Oxygen Reduction in Acid Electrolytes

In Pt-based alloy structures, selective leaching out of the non-Pt metal component (known as “dealloying)” improves catalytic activity during operation due to an increase in the electrochemically active surface area. This indicates that in Pt-based alloy structures, an electrochemical stimulus induces structural change, and the non-Pt component plays an important role in determining the catalytic performance. In this study, we prepared highly active and durable Pd@Cu@Pt core–shell catalysts for an acidic oxygen reduction reaction by a facile method and elucidated the correlation between performance improvement and repetitive potential cycling beyond a simple dealloying effect. Electrochemical activation induces the formation of a localized PtCu alloy, which is strongly correlated with excellent catalytic activity and durability (mass activity after durability test: 2.6 A mg–1Pt), on the surface and subsurface via atomic rearrangement. The origin of such catalytic activity and durability is determined by synchrotron X-ray spectroscopy, electrochemical analysis, and density functional theory calculations

Highly Efficient Bifacial Dye-Sensitized Solar Cells Employing Polymeric Counter Electrodes

Dye-sensitized solar cells (DSCs) are promising solar energy conversion devices with aesthetically favorable properties such as being colorful and having transparent features. They are also well-known for high and reliable performance even under ambient lighting, and these advantages distinguish DSCs for applications in window-type building-integrated photovoltaics (BIPVs) that utilize photons from both lamplight and sunlight. Therefore, investigations on bifacial DSCs have been done intensively, but further enhancement in performance under back-illumination is essential for practical window-BIPV applications. In this research, highly efficient bifacial DSCs were prepared by a combination of electropolymerized poly­(3,4-ethylenedioxythiphene) (PEDOT) counter electrodes (CEs) and cobalt bipyridine redox ([Co­(bpy)₃]^3+/2+) electrolyte, both of which manifested superior transparency when compared with conventional Pt and iodide counterparts, respectively. Keen electrochemical analyses of PEDOT films verified that superior electrical properties were achievable when the thickness of the film was reduced, while their high electrocatalytic activities were unchanged. The combination of the PEDOT thin film and [Co­(bpy)₃]^3+/2+ electrolyte led to an unprecedented power conversion efficiency among bifacial DSCs under back-illumination, which was also over 85% of that obtained under front-illumination. Furthermore, the advantage of the electropolymerization process, which does not require an elevation of temperature, was demonstrated by flexible bifacial DSC applications

Influence of TiO₂ Particle Size on Dye-Sensitized Solar Cells Employing an Organic Sensitizer and a Cobalt(III/II) Redox Electrolyte

Dye-sensitized solar cells (DSSCs) are highly efficient and reliable photovoltaic devices that are based on nanostructured semiconductor photoelectrodes. From their inception in 1991, colloidal TiO₂ nanoparticles (NPs) with the large surface area have manifested the highest performances and the particle size of around 20 nm is generally regarded as the optimized condition. However, though there have been reports on the influences of particle sizes in conventional DSSCs employing iodide redox electrolyte, the size effects in DSSCs with the state-of-the-art cobalt electrolyte have not been investigated. In this research, systematic analyses on DSSCs with cobalt electrolytes are carried out by using various sizes of NPs (20–30 nm), and the highest performance is obtained in the case of 30 nm sized TiO₂ NPs, indicating that there is a reversed power conversion efficiency trend when compared with those with the iodide counterpart. Detailed investigations on various factorslight harvesting, charge injection, dye regeneration, and charge collectionreveal that TiO₂ particles with a size range of 20–30 nm do not have a notable difference in charge injection, dye regeneration, and even in light-harvesting efficiency. It is experimentally verified that the superior charge collection property is the sole origin of the higher performance, suggesting that charge collection should be prioritized for designing nanostructured TiO₂ photoelectrodes for DSSCs employing cobalt redox electrolytes