Mixed Copper States in Anodized Cu Electrocatalyst for Stable and Selective Ethylene Production from CO₂ Reduction

Oxygen–Cu (O–Cu) combination catalysts have recently achieved highly improved selectivity for ethylene production from the electrochemical CO₂ reduction reaction (CO₂RR). In this study, we developed anodized copper (AN-Cu) Cu­(OH)₂ catalysts by a simple electrochemical synthesis method and achieved ∼40% Faradaic efficiency for ethylene production, and high stability over 40 h. Notably, the initial reduction conditions applied to AN-Cu were critical to achieving selective and stable ethylene production activity from the CO₂RR, as the initial reduction condition affects the structures and chemical states, crucial for highly selective and stable ethylene production over methane. A highly negative reduction potential produced a catalyst maintaining long-term stability for the selective production of ethylene over methane, and a small amount of Cu­(OH)₂ was still observed on the catalyst surface. Meanwhile, when a mild reduction condition was applied to the AN-Cu, the Cu­(OH)₂ crystal structure and mixed states disappeared on the catalyst, becoming more favorable to methane production after few hours. These results show the selectivity of ethylene to methane in O–Cu combination catalysts is influenced by the electrochemical reduction environment related to the mixed valences. This will provide new strategies to improve durability of O–Cu combination catalysts for C–C coupling products from electrochemical CO₂ conversion

Selective CO₂ Reduction on Zinc Electrocatalyst: The Effect of Zinc Oxidation State Induced by Pretreatment Environment

Here, we have developed porous nanostructured Zn electrocatalysts for CO₂ reduction reaction (CO₂RR), fabricated by reducing electrodeposited ZnO (RE-Zn) to activate the CO₂RR electrocatalytic performance. We discovered that the electrochemical activation environment using CO₂-bubbled electrolyte during reducing ZnO in a pretreatment step is important for highly selective CO production over H₂ production, while using Ar gas bubbling instead can lead to less CO product of the Zn-based catalyst in CO₂RR later. The RE-Zn activated in CO₂-bubbled electrolyte condition achieves a Faradaic efficiency of CO production (FE_CO) of 78.5%, which is about 10% higher than that of RE-Zn activated in Ar-bubbled electrolyte. The partial current density of CO product had more 10-fold increase with RE-Zn electrodes than that of bulk Zn foil at −0.95 V vs RHE in KHCO₃. In addition, a very high FE_CO of 95.3% can be reached using the CO₂-pretreated catalyst in KCl electrolyte. The higher amount of oxidized zinc states has been found in the high performing Zn electrode surface by high-resolution X-ray photoelectron spectroscopy studies, which suggest that oxidized zinc states induce the active sites for electrochemical CO₂RR. Additionally, in pre- and post-CO₂RR performance tests, the carbon deposition is also significantly suppressed on RE-Zn surfaces having a higher ratio of oxidized Zn state

Achieving 14.4% Alcohol-Based Solution-Processed Cu(In,Ga)(S,Se)₂ Thin Film Solar Cell through Interface Engineering

An optimization of band alignment at the p–n junction interface is realized on alcohol-based solution-processed Cu­(In,Ga)­(S,Se)₂ (CIGS) thin film solar cells, achieving a power-conversion-efficiency (PCE) of 14.4%. To obtain a CIGS thin film suitable for interface engineering, we designed a novel “3-step chalcogenization process” for Cu_2–<i>x</i>Se-derived grain growth and a double band gap grading structure. Considering S-rich surface of the CIGS thin film, an alternative ternary (Cd,Zn)S buffer layer is adopted to build favorable “spike” type conduction band alignment instead of “cliff” type. Suppression of interface recombination is elucidated by comparing recombination activation energies using a dark <i>J</i>–<i>V</i>–<i>T</i> analysis

Sloughing a Precursor Layer to Expose Active Stainless Steel Catalyst for Water Oxidation

Hydrogen production by water electrolysis has been regarded as a promising approach to wean away from sourcing energy through fossil fuels, as the produced hydrogen gas can be converted to electrical or thermal energy without any harmful byproducts. However, an efficient hydrogen production is restricted by the sluggish oxygen evolution reaction (OER) at the counter anode. Therefore, the development of new OER catalysts with high catalytic activities is crucial for high performance water splitting. Here, we report a novel sloughing method for the fabrication of an efficient OER catalyst on a stainless steel (SS) surface. A chalcogenide (Fe–S) overlayer generated by sulfurization on the SS surface is found to play a critical role as a precursor layer in the formation of an active surface during water oxidation. Interestingly, a newly exposed catalytic layer after sloughing off the Fe–S overlayer has a nanoporous structure with changed elemental composition, resulting in a significant improvement in OER performance with an overpotential value of 267 mV at a current density of 10 mA cm^–2 (in 1 M KOH). Our novel method for the preparation of OER catalyst provides an important insight into designing an efficient and stable electrocatalyst for the water splitting community

Synthesis of TiO₂ Nanoparticle-Embedded SiO₂ Microspheres for UV Protection Applications

Exposure to ultraviolet (UV) radiation induces many serious health issues. Because of serious health concerns, there is an urgent need to develop UV filters with better efficacy and high safety. For this purpose, titanium dioxide (TiO2) nanoparticles are the most desirable materials due to their excellent UV protection abilities. The use of TiO2 as sunscreens has raised some concerns about potential risks due to the formation of TiO2-mediated free radicals. Herein, TiO2 nanoparticles have been successfully embedded in silica (SiO2) microspheres using the emulsion synthesis method. The as-synthesized TiO2 nanoparticles embedded in silica microspheres have shown excellent UV protection ability. TiO2 nanoparticles embedded in silica microspheres suppress the photocatalytic properties compared to bare TiO2 nanoparticles, and these results indicate that TiO2-embedded silica microspheres are promising UV protection materials for sunscreen