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Although the efficiency of inorganic-organic perovskite solar cells (PSCs) has increased significantly owing to intermediate phase induced slow crystallization using dimethyl sulfoxide (DMSO) as a co-solvent in N2-filled glovebox, PSCs are generally fabricated in ambient air via a fast crystallization process to protect the perovskite layer from H2O or O2. In this study, we suggest a possibility of slow crystallization process for MAPbI3 perovskite crystals via intermediate phase formation by adjusting the humidity of air at RH 20%–30%. We obtained high-quality perovskite grains by implementing the slow crystallization process using an antisolvent and the ratio of PbI2:MAI:DMSO in the precursor solution at RH 20%–30%. The amount and state of the intermediate phase inside the as-deposited film were analyzed by grazing incidence wide-angle X-ray scattering (GIWAXS) measurements. The deposited perovskite layer with the pure intermediate via extremely slow crystallization showed higher absorption, fewer grain boundaries, and suppressed defect recombination losses than the fast crystallized perovskite phase. Thus, we obtained higher stability and high power conversion efficiency of up to 18.56% in a p-i-n-structured MAPbI3-based perovskite solar cell under ambient air with RH 20%–30%.

Pt–Ni alloy nanocrystals with Pt‐enriched shells were prepared by selective etching of surface Ni using sulfuric acid and hydroquinone. The changes in the electronic and geometric structure of the alloy nanoparticles at the surface were elucidated from the electrochemical surface area, the potential of zero total charge (PZTC), and relative surface roughness, which were determined from CO‐ and CO2‐displacement experiments before and after 3000 potential cycles under oxygen reduction reaction conditions. While the highest activity and durability were achieved in hydroquinone‐treated Pt–Ni, sulfuric acid‐treated one showed the lower activity and durability despite its higher surface Pt concentration and alloying level. Both PZTC and Q CO 2 /Q CO ratio (desorption charge of reductively adsorbed CO2 normalized by COad‐stripping charge) depend on surface roughness. In particular, Q CO 2 /Q CO ratio change better reflects the roughness on an atomic scale, and PZTC is also affected by the electronic modification of Pt atoms in surface layers. In this study, a comparative study is presented to find a relationship between surface structure and electrochemical properties, which reveals that surface roughness plays a critical role to improve the electrochemical performance of Pt–Ni alloy catalysts with Pt‐rich surfaces.

Despite the high energy density of layered-type cathode materials for Na-ion batteries, their two-dimensional crystal structure suffers a large volume change and phase transition during Na+ de/intercalation, which often results in their poor cycling performances. Thus, a robust three-dimensional framework with minimal structural change is required for stable electrochemical sodium storage. Here, we introduce an earth-abundant element-based trigonal-type Na–Fe–F compound (Na2Fe2F7) with three-dimensionally interconnected FeF6 octahedra and three-dimensional Na+ diffusion pathways. Through combined studies using first-principles calculations and experiments, we confirm that Na2Fe2F7 delivers excellent power-capability due to large three-dimensional Na+ diffusion pathways as well as ultra-long cycling performance due to negligible structural change during Na+ de/intercalation. These results will guide new insights for material discovery for high performance rechargeable batteries.

Mesoporous carbon derived from pyrolysis of metal–organic frameworks (MOFs) is advantageous owing to its high specific surface area, large pore volume, and versatility in both structure and composi...

High energy ball-milled iron sulfides with thin carbon layer coating (BM-FeS/C composites) were prepared by the simple and economical process. Ball-milled process, followed by carbon coating, reduced the particle size and increased the electrical conductivity. When employed as sodium-ion battery anodes, BM-FeS/C composites showed extremely high electrochemical performance with reversible specific capacity of 589.8 mAh·g−1 after 100 cycles at a current density of 100 mA·g−1. They also exhibited superior rate capabilities of 375.9 mAh·g−1 even at 3.2 A·g−1 and 423.6 mAh·g−1 at 1.5 A·g−1. X-ray absorption near edge structure analysis confirmed the electrochemical pathway for conversion reaction of BM-FeS/C composites.

Sodium-ion batteries (SIBs) require the development of novel anode materials due to the incompatibility of graphite anode. Herein, we explore the titanosilicate Na2Ti2O3SiO4·2H2O (STOS) as a potential anode material for SIBs. Controlling the content of crystal water in the lattice of STOS through dehydration significantly enhanced its electrochemical performances including coulombic efficiency, reversible capacity, cyclic stability and rate capability. By combining various structural analyses, the mechanism behind the enhancement was successfully clarified. Upon dehydration, the host framework is rearranged to create extra diffusion channels along the a and b axes as well as the additional vacant sodium sites previously occupied by crystal water in the original channels. Compared with the one-directional channels along the c axis in STOS, the channel of dehydrated homologue is three-dimensional with larger space finally enabling rapid sodium-ion diffusion and higher reversible capacity with the relieved lattice strains during charge/discharge. This strategy opens a new avenue and can be broadly applied to other electrode materials containing crystal water in the lattice to not only uncover their hidden potential but also suggest new realm of electrode materials for alkali ion batteries.

Scanning transmission X-ray microscopy (STXM) with ~30-nm spatial resolution revealed at annealing effect on the metal-organic interface of an Al layer with a poly (3-hexylthiophene) (P3HT) organic semiconducting layer with and without phenyl-C61-butyric acid methyl ester (PCBM). In the case of a P3HT/Al layer with a high-tensile-strain organic over-layer, the overall interface changed to a zagged morphology with Al nano pillars after thermal annealing. On the contrary, a P3HT:PCBM/Al layer with a less-tensile-strain organic over-layer showed a smooth interface except for a few nano pillars. These interfacial morphology changes were related to the initial strain status and to the relaxation process and the phase separation of P3HT crystals relating to the PCBM. Grazing-incident wide-angle X-ray scattering (GI-WAXS) measurements were also conducted to examine the residual strain and the crystalline properties of P3HT in the presence of PCBM.

Polarization curves of membrane electrode assemblies (MEAs) containing carbon-supported platinum (Pt/C) and platinum–nickel alloy (Pt 1 Ni 1 /C) as cathode catalysts were obtained for durability test as a function of time over 1100 h at constant current. Charge transfer resistance was measured using electrochemical impedance spectroscopy and postmortem analysis such as X-ray diffraction and high-resolution transmission electron microscopy was conducted in order to elucidate the degradation factors of each MEA. Our results demonstrate that the reduced performance of MEAs containing Pt 1 Ni 1 /C as a cathode catalyst was due to decreased oxygen reduction reaction caused by the corrosion of Ni, whereas that of MEAs containing Pt/C was because of reduced electrochemical surface area induced by increased Pt particle size.

The PtRu alloying degree was controlled by mixing various amounts of water in the solvent while the nominal Pt/Ru ratio was remained at the value of one, and the relationship between the alloying degree and electrochemical activities was examined in this study. X-ray diffraction analysis showed that the fraction of the alloyed Ru ranged from approximately 18% for 100% water solvent to 86% for 0% water solvent. In X-ray photoelectron spectroscopy (XPS), Pt and Ru metallic components increased with the PtRu alloying degree. Electrochemical activities for CO oxidation and methanol oxidation were enhanced as the PtRu alloying degree became higher. Electrochemical stability was also investigated via potential cycling in a methanol-contained electrolyte solution. After the potential cycling process, the catalysts were analyzed by transmission electron microscopy, XPS, XPS element mapping. Possible reasons for the difference in the electrochemical stability of the catalysts were discussed.

Carbon-supported Pt–Ni alloy nanoparticles with various compositions were prepared by a borohydride reduction method in anhydrous ethanol solvent. Here, we surveyed effect of thermally induced de-alloying on activity of the oxygen reduction reaction (ORR). Especially, changes in surface and bulk structures were investigated through electrochemical and spectroscopic measurements. The activity of as-prepared Pt–Ni alloy nanoparticles showed a monotonous dependence on Pt content. However, heat-treatment induced the phase separation between Pt and NiO and the resultant enhancement in ORR activity without significant increase in surface Pt concentration. Keywords: Pt–Ni, Oxygen reduction reaction, Fuel cell, Electrocatalyst

PtRu overlayer structures were deposited on the surface of carbon-supported Au nanoparticles with atomic-scale thicknesses and their activity for methanol electro-oxidation was examined. The results of transmission electron microscopy, X-ray diffraction, and cyclic voltammetry demonstrated that the PtRu deposited uniformly on Au nanoparticles. The peak potential in CO stripping analysis shifted to higher potentials with decreasing amounts of PtRu, indicating stronger Pt–CO and Ru–CO bonding. PtRu utilization was enhanced with decreasing PtRu, which might be attributed to the overlayer structures on Au substrates. In methanol electro-oxidation, a negative effect of the strengthened Pt–CO and Ru–CO bonding on surface specific activity and a positive effect of PtRu utilization on mass specific activity might contribute competitively to overall activity for methanol electro-oxidation.

Fuel cells are expected to be one of the major clean new energy sources in the near future. However, the slow kinetics of electrocatalytic hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR), and the high loading of Pt for the anode and cathode material are the urgent issues to be addressed since they determine the efficiency and the cost of this energy source. In this review paper, a new approach was developed for designing electrocatalysts for the HOR and ORR in fuel cells. It was found that the electronic properties of Pt could be fine-tuned by the electronic and geometric effects introduced by the substrate alloy metal and the lateral effects of the neighboring metal atoms. The role of substrate was found reflected in a volcano plot for the HOR and ORR as a function of their calculated d-band centers. This paper demonstrated a viable way to designing the electrocatalysts which could successfully alleviate two issue facing the commercializing of the fuel cell-the cost of electrocatalysts and their efficiency.

Electrocatalysts for hydrogen oxidation reactions (HORs) are the key to renewable-energy technologies including fuel cells, hydrogen pumps, and water splitting. Despite the significant technological interest and tremendous efforts that have been made, development of hydrogen electrode catalysts with high activity at low cost remains a great challenge. Here, we report the preparation, characterization, and electrochemical properties of a hybrid material composed of Pd nanocrystals grown on spontaneously oxidized WC as a high-performance catalyst for the HOR. The Pd/WC hybrid exhibits enhanced catalytic activity compared to a carbon supported Pd (Pd/C) catalyst, making it a Pt-free, effective catalyst for the HOR. The remarkable catalytic activity arises from synergistic ligand effects between Pd and WC.

A physical synthesis of multilayered Pt/Ru nanorods with controllable bimetallic sites as methanol oxidation catalysts is reported for the first time. The novel nanorods were synthesized via the oblique angle deposition method, deposited prior to the formation of each individual noble metal layer, in a sequential fashion. It has been shown that the oblique angle deposition controls the morphology and electrochemical properties of the resultant nanostructures. Sequentially the multilayered nanorods comprising Pt and Ru segments exhibited superior electrocatalytic activity when compared to equivalent monometallic Pt nanorods with respect to methanol electrooxidation reaction in an acidic medium. Moreover, it has been established that the electrochemical process takes place at the Pt/Ru nanorods followed the bifunctional mechanism. The relative rates of reaction, recorded using chronoamperometry, show a linear relationship between the long-time current density and the number of Pt/Ru interfaces. Interestingly, the best catalyst for methanol oxidation was found to the surface of bimetallic Pt/Ru nanorods produced by the heat treatments via the so-called electronic effect. This reflects the fact that the ensemble effects of combined bifunctional and electronic effects via second elements could be expected in methanol oxidation reactions. Electrocatalytic activities correlate well with bimetallic pair sites and electronic properties analyzed by X-ray photoemission spectroscopy and X-ray absorption near-edge structure.

Size-controlled Pt nanocatalysts embedded in TiO(2) were successfully synthesized by simultaneous dual-gun sputtering and were found to exhibit unique electronic properties depending on their size, which affected the potential of zero total charge, CO-bulk oxidation, and methanol oxidation reaction.

Titanium dioxide nanotube (TONT) arrays grown by electrochemical anodization were used as supports for alloyed PtNi catalysts which were developed by a cosputtering technique. The as-deposited PtNi on TONT had poor oxygen reduction reaction (ORR) activity with a significant overpotential, while the ORR activity of annealed PtNi/TONT was improved. The maximum ORR activity, with a significant increase (120 mV) of the half-wave potential, was achieved for 400°C annealed PtNi/TONT. This favorable enhancement was attributable to two factors. The first is the formation of a PtNi alloy catalyst, which resulted in the modification of the d-electronic structure of Pt, leading to the favorable adsorption of O 2 . The second factor is a strong metal-support interaction (SMSI) effect. When the high-temperature thermal treatment was conducted in the reducing gas (hydrogen gas) on the PtNi/TONT, there was electron transfer from the reduced support to the Pt catalyst. This caused a change of the work function that altered the electronic properties of surface Pt atoms (X-ray photoemission spectroscopy measurement), leading to an enhancement of the ORR activity. To investigate the SMSI effect further, the thin Pt/TONT samples were prepared and used for the investigation of the interfacial region between the TONT support and the Pt catalyst.