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High entropy alloys (HEAs) are encapsulated in graphitized hollow carbon tubes to confine the growth of alloy particles during the formation process. Zinc–air batteries with HEAs as air electrodes exhibit long-lasting durability and high efficiency.

The preparation of low-cost, simple, and scalable electrodes is crucial for the commercialization of water electrolyzers for H2 production. Herein, we demonstrate the fabrication of cathodes through Mo-modified Zn phosphating of Ni foam (NiF) for water electrolysis, which has been largely utilized in surface coating industry. In situ growth of electrocatalytically active layers in the hydrogen evolution reaction (HER) was occurred after 1 min of phosphating to form ZnNiMoPi, and subseque activation resulted in the formation of ZnNiMoPOxHy. ZnNiMoPOxHy exhibited superior HER performance than NiF, primarily because of the increased electrochemically active surface area of ZnNiMoPOxHy compared to that of bare NiF. Although further investigations to improve the intrinsic electrochemical activity toward the HER and detailed mechanistic studies are required, these results suggest that phosphating is a promising coating method and will possibly advance the fabrication procedure of electrodes for water electrolyzers with better practical applications.

Photoelectrochemical cells represent one of the promising ways to renewably produce hydrogen (H2) as a future chemical fuel. The design of a catalyst/semiconductor junction for the hydrogen evolution reaction (HER) requires various factors for high performance. In catalytic materials, an intrinsic activity with fast charge-transfer kinetics is important. Additionally, their thermodynamic property and physical adhesion should be compatible with the underlying semiconductor for favorable band alignment and stability during vigorous H2 bubble formation. Moreover, catalysts, especially non-noble materials that demand a large amount of loading, should be adequately dispersed on the semiconductor surface to allow sufficient light absorption to generate excitons. One of the methods to simultaneously satisfy these conditions is to adopt an interfacial layer between the semiconductor and active materials in HER. The interfacial layer efficiently extracts the electrons from the semiconductor and conveys those to the catalytically active surface. We demonstrate Ag as a 3D interfacial nanostructure of patterned MoSx catalysts for photoelectrochemical HER. The nanostructured porous Ag layer was introduced by a simple chemical process, followed by photoelectrochemical deposition of MoSx to form MoSx/Ag nanostructures in cross-shaped catalyst pattern arrays. Ag modulated the surface electronic property of MoSx to improve the reaction kinetics as well as helped a charge transport at the Ag|p-Si(100) junction. The physically stable adhesion of catalysts was also achieved despite the ∼40 nm thick catalysts owing to the interfacial Ag nanostructure. This work contributes to further understand the complex multistep HER from light absorption to charge transfer to protons, helping to develop cost-effective and efficient photocathodes.

To minimize the utilization of fossil fuels, the demand for H2 production through water electrolysis has considerably increased. NiFeOxHy-based electrocatalysts have attracted extensive attention o...

In this work, the structure and electrochemical properties of titanate ceramics with in situ Ni exsolution are investigated to identify the structure-performance relationship of the exsolved perovskite for use as electrode materials in solid oxide cells. The phase formation, redox behaviour and exsolution properties of the material have been studied. The characteristics of the individual electrochemical processes are identified and correlated with the Ni doping and microstructural evolution. The results indicate that the electrode activity is strongly dependent on the density and particle size of the in situ grown Ni nanoparticles. The interfacial ion transfer and charge transfer processes can be promoted by increasing the electrode surface area or improving the adhesion between the electrode and electrolyte, while the surface electrode processes including the dissociative adsorption are more dependent on the porosity and electrode/electrolyte interfacial region of the exsolved titanate electrode.

Developing robust oxygen evolution reaction (OER) electrocatalysts with excellent performance is essential for the conversion of renewable electricity to clean fuel. Herein, we present a facile concept for the synthesis of efficient high-entropy metal-organic frameworks (HEMOFs) as electrocatalysts in a one-step solvothermal synthesis. This strategy allows control of the microstructure and corresponding lattice distortion by tuning the metal ion composition. As a result, the OER activity was improved by optimizing the coordination environment of the metal catalytic center. The optimized Co-rich HEMOFs exhibited a low overpotential of 310 mV at a current density of 10 mA cm

The release of microplastics (MPs) into the environment has engendered considerable ecosystem and human health concerns. Herein, we propose light-driven photocatalytic upcycling of MPs using heterojunction photocatalysts. A novel synthesis method was developed through in-situ conversion of unstable metal sites on bimetallic metal-organic frameworks (MOF), resulting in nanometer-sized particles with semiconductor properties which are confined into the framework of MOFs to prevent agglomeration. These modified MOF can be used for photocatalytic conversion of MPs along with hydrogen (H2) production. As a proof of concept, FeAg-MOF was selected as a precursor to fabricate Ag2O/Fe-MOF photocatalysts. Light illumination induced the formation of Ag2O with a particle size of ∼6 nm into MOF framework structure. The Ag2O/Fe-MOF displays a broad solar light-harvesting range with exposed active sites. Furthermore, band-matching the Ag2O/Fe-MOF heterojunction can enable the conversion of MPs into value-added chemicals, accompanied by H2 production. The present work provides an insight into designing advanced heterojunction photocatalysts and converting MPs into value-added chemicals, coupled with clean energy production.

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Photoelectrochemical cells represent one of the promising ways to renewably produce hydrogen (H

Although NiFeOxHy has attracted enormous attention as an alkaline water electrolyzer owing to its high performance in the oxygen evolution reaction (OER), it still requires further improvement in t...

Platinum is still the most active element for the hydrogen evolution reaction (HER); however, it suffers from its scarcity and high cost. Thus, significant efforts have been dedicated to maximize the catalytic activity with less loading. When Pt is utilized at a semiconductor surface, more factors have to be considered. Placing a catalyst directly in contact with a semiconductor supports the extraction of photogenerated minority carriers as well as boosts the catalytic reactions. In addition, a catalyst should be designed with prudence not to interfere in the light path with respect to absorption at the underlying substrate. Herein, we report the development of planar Si-based photocathodes, covered with a native oxide, for the HER, which also satisfy the prerequisites for the use of a three-dimensionally patterned, flower-like Ag–Pt catalyst. The catalyst consisted of nanoparticles of homogeneously alloyed Ag and Pt, fabricated by a galvanic exchange of Pt with Ag. Importantly, these two elements were proven to have their own functionalities. Ag not only contributed to transporting e− and Had to the Pt for subsequent processes of the HER but also effectively extracted minority carriers by diluting the high work function of Pt, leading to a better Schottky barrier at the catalyst–insulator–semiconductor junction. Furthermore, computational simulation revealed that the proposed catalyst pattern alleviated optical light loss with the increasing catalyst loading compared to the two-dimensional case. Owing to these effects, we could achieve 0.36 V (vs. reversible hydrogen electrode) as an open circuit potential and the near maximum current density of planar p-type Si. The findings in this work suggests deeper insights that could support the design of catalysts for solar-fuel systems.

Light addressable/activated electrochemistry (LAE) has recently attracted attention as it can provide spatially resolved electrochemical information without using pre-patterned electrodes whose sizes and positions are unchangeable. Here, we propose hematite (α-Fe2O3) as the photoanode for LAE, which does not require any sort of surface modification for protection or facilitating charge transfer. As experimentally confirmed with various redox species, hematite is stable enough to be used for repetitive electroanalytical measurements. More importantly, it offers exceptionally high spatial resolution so that the “virtual electrode” is exactly as large as the light spot owing to the short diffusion length of the minority carriers. Quantitative analysis of dopamine in this study shows that the hematite-based photoanode is a promising platform for many potential LAE applications including spatially selective detection of oxidizable biomolecules.

Lowering the cost of electrocatalysts for the oxygen reduction reaction (ORR) is indispensable for the wider commercialization of fuel cells. Therefore, the development of non-Pt, especially metal-free, carbon-based electrocatalysts, has been encouraged as an alternative to Pt. Here, we report active N-doped nanocarbon electrocatalysts in ORR activated by thermal treatment of pristine carbon precursors with highly aligned mesopore channels under an NH3 atmosphere. This NH3-activation process adopts N-containing carbon sites, leading to enhanced ORR performance in an alkaline electrolyte with negligible formation of peroxide species. The stability of the activated carbon electrocatalysts was confirmed by performing 40,000 rounds of potential cycles in the accelerated stress test (AST). The variations in the voltammograms during AST were analyzed using X-ray photoelectron spectroscopy. The correlation between electrochemical behavior and the N 1 s spectrum corroborates the contribution of N-related sites toward voltammetric responses in ORR.

The utilization of solar energy for CO2 reduction reaction (CO2RR) into valuable hydrocarbons offers attractive solution towards low-carbon future, but their performance is affected by the competing hydrogen evolution reaction (HER) that occurs simultaneously. Herein, we proposed maximizing interface integration and surface reconstructing engineer strategy to improve the CO2RR activity and selectivity of heterojunction photocatalyst. A surface-reconstructed ZnO/CuOx catalysts are uniformly anchored on the porous carbon nanosheet arrays that are supported by carbon nanofibers (ZnO/CuOx-C CNFs). Downsizing ZnO/CuOx maximizes the interface integration of components to promote electron-hole pairs separation and increase surface active site density. Moreover, the surface reconstruction (the formation of the hydroxyl groups on ZnO via facile light irradiation) promotes the kinetic of CO2RR to CH4 and oxygen evolution reaction (OER), while depressing the competing HER and CO generation. All these advantages contribute to the excellent catalytic performance: a high CH4 generation rate of 241.6 μmol h−1 g−1 with the selectivity of ∼96 % for ZnO/CuOx-C CNFs under full light irradiation. The insight into the modification of photocatalyst structure and mechanism investigation pave the way for a new design strategy to advance solar photocatalytic technology for CO2 reduction.

Expedited conversion of O2 to H2O with minimal amounts of Pt is essential for wide applicability of PEM fuel cells (PEMFCs). Therefore, it is imperative to develop a process for catalyst management to circumvent unnecessary catalyst loss while improving the Pt utilization, catalytic activity, and durability. Here, the fabrication of a self‐standing nanofiber electrode is demonstrated by employing electrospinning. This film‐type catalyst simultaneously contains Pt–Co alloy nanoparticles and Co embedded in an N‐doped graphitized carbon (Co–Nx) support derived from the electrospun zeolitic imidazolate frameworks. Notably, the flexible electrode is directly transferrable for the membrane‐electrode assembly of high temperature PEMFC. In addition, the electrodes exhibit excellent performance, maybe owing to the synergistic interaction between the Pt–Co and Co–Nx as revealed by the computational modeling study. This method simplifies the fabrication and operation of cell device with negligible Pt loss, compared to ink‐based conventional catalyst coating methods.

Light addressable/activated electrochemistry (LAE) has recently attracted attention as it can provide spatially resolved electrochemical information without using pre-patterned electrodes whose sizes and positions are unchangeable. Here, we propose hematite (α-Fe

Hydrogen is in the lime light as a carbon-free alternative energy source due to its high energy conversion efficiency. Solar-driven water splitting is one of the most promising methods for renewable hydrogen production. However, commercialization of a photoelectrochemical hydrogen production system remains a great challenge. One of the emerging concerns is the development of an inexpensive and transparent catalyst, which does not obstruct the light pathways to the semiconductor electrode. Here we report a non-noble metal electrocatalyst for hydrogen evolution, Ni-Mo, which is directly patterned on amorphous Si (a-Si) by light-guided spatially selective electrodeposition without consecutive photolithography processes. A light pattern is illuminated onto the a-Si using a digital micromirror device to commence the photoelectrochemical deposition. The catalyst patterned by the proposed method not only admits sufficient light to a-Si but also enables long distance carrier transport along the inversion layer, as previously observed in crystalline Si (c-Si) photocathodes. This new electrodeposition method enables mask-free patterning on a-Si and is expected to expedite a lower cost, more efficient, and self-biasing integrated photoelectrochemical water-splitting device.

For more efficient photoelectrochemical water splitting, there is a dilemma that a photoelectrode needs both light absorption and electrocatalytic faradaic reaction. One of the promising strategies is to deposit a pattern of electrocatalysts onto a semiconductor surface, leaving sufficient bare surface for light absorption while minimizing concentration overpotential as well as resistive loss at the ultramicroelectrodes for faradaic reaction. This scheme can be successfully realized by “maskless” direct photoelectrochemical patterning of electrocatalyst onto an SiOx/amorphous Si (a-Si) surface by the light-guided electrodeposition technique. Electrochemical impedance spectroscopy at various pHs tells us much about how it works. The surface states at the SiOx/a-Si interface can mediate the photogenerated electrons for hydrogen evolution, whereas electroactive species in the solution undergo outer-sphere electron transfer, taking electrons tunneling across the SiOx layer from the conduction band. In additio...

B. J. Kim, Y.-R. Kim, S. Y. Lim, J. H. Bae, Prof. T. D. Chung Department of Chemistry Seoul National University Seoul, 151-747, Republic of Korea 2E-mail: tdchung@snu.ac.krD.-J. Lee, Prof. K.-B. Kim Department of Materials Science and Engineering and Research Institute of Advanced Materials (RIAM) Seoul National University Seoul, 151-747, Republic of Korea made was superior in conductivity (with estimated resistivity of E-mail: kibum@snu.ac.krProf. K.-B. Kim WCU Hybrid Materials Program Department of Materials Science and Engineering Seoul National University Seoul 151-747, Republic of Korea

Silicon dioxide thin films are widely used as dielectric layers in microelectronics and can also be engineered on silicon wafers. It seems counterintuitive that electrochemical reactions could occur on such an insulator without relying on tunnelling current. Here we report electrochemistry based on electron transfer through a thin insulating layer of thermally grown silicon dioxide on highly n-doped silicon. Under a negative electrical bias, protons in the silicon dioxide layer were reduced to hydrogen atoms, which served as electron mediators for electrochemical reduction. Palladium nanoparticles were preferentially formed on the dielectric layer and enabled another hydrogen-atom-mediated electrochemistry, as their surfaces retained many electrogenerated hydrogen atoms to act as a 'hydrogen-atom reservoir' for subsequent electrochemical reduction. By harnessing the precisely controlled electrochemical generation of hydrogen atoms, palladium-copper nanocrystals were synthesized without any surfactant or stabilizer on the silicon dioxide layer.

The highly selective electrochemical reduction of carbon dioxide (CO2) is reported to formate (HCOO-) at a compactly integrated bioelectrode. The enzymatic biocatalytic cathode is fabricated by single-step electropolymerization of a multifunctional polydopamine film in which enzyme/cofactor couples are uniquely embedded. Interestingly, this thin biohybrid system of nanoscale thickness assures unprecedentedly prolonged catalytic enzyme stability for about two weeks. Mimicking the natural photosynthesis, combination with the photoanode utilizing the water oxidation, steadily produces formate at a faradaic efficiency of 99.18 ± 6.77% with little degradation at least for 1 d under 1 sun illumination and no external bias.

We have devised a unique method for sensitive and selective detection of Hg(2+) ions using DNA-modified gold microshells which can be individually manipulated using a micropipette and act as a micro SERS probe for analysis in small sample volumes.