Chemical-Reductant-Free Electrochemical Deuteration Reaction using Deuterium Oxide

We report a method for the electrochemical deuteration of α,β-unsaturated carbonyl compounds under catalyst- and external-reductant-free conditions, with deuteration rates as high as 99 % and yields up to 91 % in 2 h. The use of graphite felt for both the cathode and the anode was key to ensuring chemoselectivity and high deuterium incorporation under neutral conditions without the need for an external reductant. This method has a number of advantages over previously reported deuteration reactions that use stoichiometric metallic reductants. Mechanistic experiments showed that O₂ evolution at the anode not only eliminates the need for an external reductant but also regulates the pH of the reaction mixture, keeping it approximately neutral.     

Electrochemical Preparation of N‐Doped Cobalt Oxide Nanoparticles with High Electrocatalytic Activity for the Oxygen‐Reduction Reaction

Nitrogen‐doped CoO (N‐CoO) nanoparticles with high electrocatalytic activity for the oxygen‐reduction reaction (ORR) were fabricated by electrochemical reduction of CoCl₂ in acetonitrile solution at cathodic potentials. The initially generated, highly reactive nitrogen‐doped Co nanoparticles were readily oxidized to N‐CoO nanoparticles in air. In contrast to their N‐free counterparts (CoO or Co₃O₄), N‐CoO nanoparticles with a N content of about 4.6 % exhibit remarkable ORR electrocatalytic activity, stability, and immunity to methanol crossover in an alkaline medium. The Co?N_x active sites in the CoO nanoparticles are held responsible for the high ORR activity. This work opens a new path for the preparation of nitrogen‐doped transition metal oxide nanomaterials, which are promising electrocatalysts for fuel cells.     

High‐Resolution Electrochemical Mapping of the Hydrogen Evolution Reaction on Transition‐Metal Dichalcogenide Nanosheets

High‐resolution scanning electrochemical cell microscopy (SECCM) is used to image and quantitatively analyze the hydrogen evolution reaction (HER) catalytically active sites of 1H‐MoS₂ nanosheets, MoS₂, and WS₂ heteronanosheets. Using a 20 nm radius nanopipette and hopping mode scanning, the resolution of SECCM was beyond the optical microscopy limit and visualized a small triangular MoS₂ nanosheet with a side length of ca. 130 nm. The electrochemical cell provides local cyclic voltammograms with a nanoscale spatial resolution for visualizing HER active sites as electrochemical images. The HER activity difference of edge, terrace, and heterojunction of MoS₂ and WS₂ were revealed. The SECCM imaging directly visualized the relationship of HER activity and number of MoS₂ nanosheet layers and unveiled the heterogeneous aging state of MoS₂ nanosheets. SECCM can be used for improving local HER activities by producing sulfur vacancies using electrochemical reaction at the selected region.     

Chemical‐Bath‐Deposited Indium Oxide Microcubes for Solar Water Splitting

We fabricated films of cubic indium oxide (In₂O₃) by chemical bath deposition (CBD) for solar water splitting. The fabricated films were characterized by X‐ray diffraction analysis, Raman scattering, X‐ray photoelectron spectroscopy, and scanning electron microscopy, and the three‐dimensional microstructure of the In₂O₃ cubes was elucidated. The CBD deposition time was varied, to study its effect on the growth of the In₂O₃ microcubes. The optimal deposition time was determined to be 24 h, and the corresponding film exhibited a photocurrent density of 0.55 mA cm^?2. Finally, the film stability was tested by illuminating the films with light from an AM 1.5 filter with an intensity of 100 mW cm^?2.     

Partially Reduced Graphite Oxide as an Electrode Material for Electrochemical Double‐Layer Capacitors

Partially reduced graphite oxide was prepared from graphite oxide by using synthetic graphite as precursor. The reduction of graphite oxide with a layer distance of 0.57 nm resulted in a reduction of the layer distance depending on the degree of reduction. Simultaneously the amount of oxygen functionalities in the graphite oxide was reduced, which was corroborated by elemental analysis and EDX. The electrochemical activation of the partially reduced graphite oxide was investigated for tetraethylammonium tetrafluoroborate in acetonitrile and in propylene carbonate. The activation potential depends significantly on the degree of reduction, that is, on the graphene‐layer distance and on the solvent used. The activation potential decreased with increasing layer distance for both positive and negative activation. The resulting capacitance after activation was found to be affected by the layer distance, the oxygen functionalities and the used electrolyte. For a layer distance of 0.43 nm and with acetonitrile as the solvent, a differential capacitance of 220 Fg^?1 was achieved for the discharge of the positive electrode near the open‐circuit potential and 195 Fg^?1 in a symmetric full‐cell assembly.     

Electrochemical Label‐Free Nucleotide Sensors

Numerous researchers have devoted a great deal of effort over the last few decades to the development of electrochemical oligonucleotide detection techniques, owing to their advantages of simple design, inherently small dimensions, and low power requirements. Their simplicity and rapidity of detection makes label‐free oligonucleotide sensors of great potential use as first‐aid screening tools in the analytical field of environmental measurements and healthcare management. This review article covers label‐free oligonucleotide sensors, focusing specifically on topical electrochemical techniques, including intrinsic redox reaction of bases, conductive polymers, the use of electrochemical indicators, and highly ordered probe structures.     

Bimetallic Metal‐Organic Framework‐Derived Nanosheet‐Assembled Nanoflower Electrocatalysts for Efficient Oxygen Evolution Reaction

Non‐noble metal‐based metal–organic framework (MOF)‐derived electrocatalysts have recently attracted great interest in the oxygen evolution reaction (OER). Here we report a facile synthesis of nickel‐based bimetallic electrocatalysts derived from 2D nanosheet‐assembled nanoflower‐like MOFs. The optimized morphologies and large Brunauer–Emmett–Teller (BET) surface area endow FeNi@CNF with efficient OER performance, where the aligned nanosheets can expose abundant active sites and benefit electron transfer. The complex nanoflower morphologies together with the synergistic effects between two metals attributed to the OER activity of the Ni‐based bimetallic catalysts. The optimized FeNi@CNF afforded an overpotential of 356 mV at a current density of 10 mA cm^?2 with a Tafel slope of 62.6 mV dec^?1, and also exhibited superior durability with only slightly degradation after 24 hours of continuous operation. The results may inspire the use of complex nanosheet‐assembled nanostructures to explore highly active catalysts for various applications.     

In Situ Observation of Surface Species on Iridium Oxide Nanoparticles during the Oxygen Evolution Reaction

An iridium oxide nanoparticle electrocatalyst under oxygen evolution reaction conditions was probed in situ by ambient‐pressure X‐ray photoelectron spectroscopy. Under OER conditions, iridium undergoes a change in oxidation state from Ir^IV to Ir^V that takes place predominantly at the surface of the catalyst. The chemical change in iridium is coupled to a decrease in surface hydroxide, providing experimental evidence which strongly suggests that the oxygen evolution reaction on iridium oxide occurs through an OOH‐mediated deprotonation mechanism.     

Carbon‐Based Metal‐Free Catalysts for Electrocatalysis beyond the ORR

Besides their use in fuel cells for energy conversion through the oxygen reduction reaction (ORR), carbon‐based metal‐free catalysts have also been demonstrated to be promising alternatives to noble‐metal/metal oxide catalysts for the oxygen evolution reaction (OER) in metal–air batteries for energy storage and for the splitting of water to produce hydrogen fuels through the hydrogen evolution reaction (HER). This Review focuses on recent progress in the development of carbon‐based metal‐free catalysts for the OER and HER, along with challenges and perspectives in the emerging field of metal‐free electrocatalysis.     

Dual Role of Silver Moieties Coupled with Ordered Mesoporous Cobalt Oxide towards Electrocatalytic Oxygen Evolution Reaction

Herein, we show that the performance of mesostructured cobalt oxide electrocatalyst for oxygen evolution reaction (OER) can be significantly enhanced by coupling of silver species. Various analysis techniques including pair distribution function and Rietveld refinement, X‐ray absorption spectroscopy at synchrotron as well as advanced electron microscopy revealed that silver exists as metallic Ag particles and well‐dispersed Ag₂O nanoclusters within the mesostructure. The benefits of this synergy are twofold for OER: highly conductive metallic Ag improves the charge transfer ability of the electrocatalysts while ultra‐small Ag₂O clusters provide the centers that can uptake Fe impurities from KOH electrolyte and boost the catalytic efficiency of Co–Ag oxides. The current density of mesostructured Co₃O₄ at 1.7 V_RHE is increased from 102 to 211 mA cm^?2 with incorporation of silver spices. This work presents the dual role of silver moieties and demonstrates a simple method to increase the OER activity of Co₃O₄.     

General Self‐Template Synthesis of Transition‐Metal Oxide and Chalcogenide Mesoporous Nanotubes with Enhanced Electrochemical Performances

The development of a general strategy for synthesizing hierarchical porous transition‐metal oxide and chalcogenide mesoporous nanotubes, is still highly challenging. Herein we present a facile self‐template strategy to synthesize Co₃O₄ mesoporous nanotubes with outstanding performances in both the electrocatalytic oxygen‐evolution reaction (OER) and Li‐ion battery via the thermal‐oxidation‐induced transformation of cheap and easily‐prepared Co‐Asp(cobalt–aspartic acid) nanowires. The initially formed thin layers on the precursor surfaces, oxygen‐induced outward diffusion of interior precursors, the gas release of organic oxidation, and subsequent Kirkendall effect are important for the appearance of the mesoporous nanotubes. This self‐template strategy of low‐cost precursors is found to be a versatile method to prepare other functional mesoporous nanotubes of transition‐metal oxides and chalcogenides, such as NiO, NiCo₂O₄, Mn₅O₈, CoS₂ and CoSe₂.     

Plasma‐Engraved Co3O4 Nanosheets with Oxygen Vacancies and High Surface Area for the Oxygen Evolution Reaction

Co₃O₄, which is of mixed valences Co²⁺ and Co³⁺, has been extensively investigated as an efficient electrocatalyst for the oxygen evolution reaction (OER). The proper control of Co²⁺/Co³⁺ ratio in Co₃O₄ could lead to modifications on its electronic and thus catalytic properties. Herein, we designed an efficient Co₃O₄‐based OER electrocatalyst by a plasma‐engraving strategy, which not only produced higher surface area, but also generated oxygen vacancies on Co₃O₄ surface with more Co²⁺ formed. The increased surface area ensures the Co₃O₄ has more sites for OER, and generated oxygen vacancies on Co₃O₄ surface improve the electronic conductivity and create more active defects for OER. Compared to pristine Co₃O₄, the engraved Co₃O₄ exhibits a much higher current density and a lower onset potential. The specific activity of the plasma‐engraved Co₃O₄ nanosheets (0.055 mA cm^?2_BET at 1.6 V) is 10 times higher than that of pristine Co₃O₄, which is contributed by the surface oxygen vacancies.     

Enhanced Electrochemical Capacitive Properties of Nickel‐Cobalt Oxide Nano‐flakes Materials

Nickel‐cobalt oxide nano‐flakes materials are successfully synthesized by a facile chemical co‐precipitation method followed by a simple calcination process. The studies show that the as‐prepared nickel‐cobalt oxides with different Ni/Co ratio are composed of NiO and Co₃O₄ compounds. The Co_0.56Ni_0.44 oxide material, which exhibits a mesoporous structure with a narrow distribution of pore size from 2 to 7 nm, possesses markedly enhanced charge‐discharge properties at high current density compared with the pure NiO and pure Co₃O₄. The Co_0.56Ni_0.44 oxide electrode shows a specific capacitance value of 1227 F/g at 5 mA/cm², which is nearly three times greater than that of the pure NiO electrode at the same current density.     

Coupling Magnetic Single‐Crystal Co2Mo3O8 with Ultrathin Nitrogen‐Rich Carbon Layer for Oxygen Evolution Reaction

Transition‐metal oxides as electrocatalysts for the oxygen evolution reaction (OER) provide a promising route to face the energy and environmental crisis issues. Although palmeirite oxide A₂Mo₃O₈ as OER catalyst has been explored, the correlation between its active sites (tetrahedral or octahedral) and OER performance has been elusive. Now, magnetic Co₂Mo₃O₈@NC‐800 composed of highly crystallized Co₂Mo₃O₈ nanosheets and ultrathin N‐rich carbon layer is shown to be an efficient OER catalyst. The catalyst exhibits favorable performance with an overpotential of 331 mV@10 mA cm^?2 and 422 mV@40 mA cm^?2, and a full water‐splitting electrolyzer with it as anode catalyst shows a cell voltage of 1.67 V@10 mA cm^?2 in alkaline. Combined HAADFSTEM, magnetic, and computational results show that factors influencing the OER performance can be attributed to the tetrahedral Co sites (high spin, t₂³e⁴), which improve the OER kinetics of rate‐determining step to form *OOH.     

A Reliable Aerosol‐Spray‐Assisted Approach to Produce and Optimize Amorphous Metal Oxide Catalysts for Electrochemical Water Splitting

An aerosol‐spray‐assisted approach (ASAA) is proposed and confirmed as a precisely controllable and continuous method to fabricate amorphous mixed metal oxides for electrochemical water splitting. The proportion of metal elements can be accurately controlled to within (5±5) %. The products can be sustainably obtained, which is highly suitable for industrial applications. ASAA was used to show that Fe₆Ni₁₀O_x is the best catalyst among the investigated Fe‐Ni‐O_x series with an overpotential of as low as 0.286 V (10 mA cm^?2) and a Tafel slope of 48 mV/decade for the electrochemical oxygen evolution reaction. Therefore, this work contributes a versatile, continuous, and reliable way to produce and optimize amorphous metal oxide catalysts.     

Rose‐like Nanocomposite of Fe‐Ni Phosphides/Iron Oxide as Efficient Catalyst for Oxygen Evolution Reaction

In order to accelerate the reaction rate of water splitting, it is of immense importance to develop low‐cost, stable and efficient catalysts. In this study, the facile synthesis of a novel rose‐like nanocomposite catalyst (Ni₂P/Fe₂P/Fe₃O₄) is reported. The synthesis process includes a solvothermal step and a phosphatization step to combine iron oxides and iron‐nickel phosphides. Ni₂P/Fe₂P/Fe₃O₄ performs well in catalyzing oxygen evolution reaction, with a very low overpotential of 365 mV to reach 10 mA cm^?2 current density. The Tafel slope is as low as 59 mV dec^?1. Ni₂P/Fe₂P/Fe₃O₄ has a large double‐layer capacitance that contributes to a high electrochemically active area. Moreover, this catalyst is very stable for long‐term use. Therefore, the Ni₂P/Fe₂P/Fe₃O₄ catalyst has a high potential for use in oxygen evolution reactions.     

Improved Electrochemical Cycling Durability in a Nickel Oxide Double‐Layered Film

For the first time, a crystalline–amorphous double‐layered NiO_x film has been prepared by reactive radio frequency magnetron sputtering. This film has exhibited improved electrochemical cycling durability, whereas other electrochromic parameters have been maintained at the required level, namely, a short coloration/bleaching time (0.8 s/1.1 s) and an enhanced transmittance modulation range (62.2 %) at λ =550 nm. Additionally, the double‐layered film has shown better reversibility than that of amorphous and crystalline single‐layered films.     

Polyoxometalate and Resin‐Derived P‐Doped Mo2C@N‐Doped Carbon as a Highly Efficient Hydrogen‐Evolution Reaction Catalyst at All pH Values

A new type of P‐doped Mo₂C coated by N‐doped carbon (P‐Mo₂C@NC) has been successfully prepared by calcining a mixture of H₃[PMo₁₂O₄₀] polyoxometalates (POMs) and urea‐formaldehyde resin under an N₂ atmosphere. Urea‐formaldehyde resin not only serves as the carbon source to ensure carbonization but also facilitates the uniform distribution of POM precursors, which efficiently avoid the aggregation of Mo₂C particles at high temperatures. TEM analysis revealed that the average diameter of the Mo₂C particles was about 10 nm, which is coated by a few‐layer N‐doped carbon sheet. The as‐prepared P‐Mo₂C@NC displayed excellent hydrogen‐evolution reaction (HER) performance and long‐term stability in all pH environments. To reach a current density of 10 mA cm^?2, only 109, 159, and 83 mV were needed for P‐Mo₂C@NC in 0.5 m H₂SO₄ (pH 0), 0.1 m phosphate buffer (pH 7), and 1 m KOH (pH 14), respectively. This could provide a high‐yield and low‐cost method to prepare uniform nanosized molybdenum carbides with highly efficient and stable HER performance.     

Functional Porous Carbon/Nickel Oxide Nanocomposites as Binder‐Free Electrodes for Supercapacitors

High‐surface‐area, guava‐leaf‐derived, heteroatom‐containing activated carbon (GHAC) materials were synthesized by means of a facile chemical activation method with KOH as activating agent and exploited as catalyst supports to disperse nickel oxide (NiO) nanocrystals (average size (2.0±0.1) nm) through a hydrothermal process. The textural and structural properties of these GHAC/NiO nanocomposites were characterized by various physicochemical techniques, namely, field‐emission SEM, high‐resolution TEM, elemental analysis, X‐ray diffraction, X‐ray photoelectron spectroscopy, thermogravimetric analysis, and Raman spectroscopy. The as‐synthesized GHAC/NiO nanocomposites were employed as binder‐free electrodes, which exhibited high specific capacitance (up to 461 F g^?1 at a current density of 2.3 A g^?1) and remarkable cycling stability, which may be attributed to the unique properties of GHAC and excellent electrochemical activity of the highly dispersed NiO nanocrystals.