Single-atom nickel catalysts hold great promise for photocatalytic water splitting due to their plentiful active sites and cost-effectiveness. Herein, we adopt a reactive-group guided strategy to prepare atomically dispersed nickel catalysts on red phosphorus. The hydrothermal treatment of red phosphorus leads to the formation of P-H and P-OH groups, which behave as the reactive functionalities to generate the dual structure of single-atom P-Ni and P-O-Ni catalytic sites. The produced single-atom sites provide two different functions: P-Ni for water reduction and P-O-Ni for water oxidation. Benefitting from this specific Janus structure, Ni-red phosphorus shows an elevated hydrogen evolution rate compared to Ni nanoparticle-modified red phosphorus under visible-light irradiation. The hydrogen evolution rate was additionally enhanced with increased reaction temperature, reaching 91.51 μmol h
Usually, most studies focus on toxic gas and photosensors by using electrospinning and metal oxide polycrystalline SnO2 nanofibers (PNFs), while fewer studies discuss cell–material interactions and photoelectric effect. In this work, the controllable surface morphology and oxygen defect (VO) structure properties were provided to show the opportunity of metal oxide PNFs to convert photoenergy into bio-energy for bio-material applications. Using the photobiomodulation effect of defect-rich polycrystalline SnO2 nanofibers (PNFs) is the main idea to modulate the cell–material interactions, such as adhesion, growth direction, and reactive oxygen species (ROS) density. The VO structures, including out-of-plane oxygen defects (op-VO), bridge oxygen defects (b-VO), and in-plane oxygen defects (ip-VO), were studied using synchrotron analysis to investigate the electron transfer between the VO structures and conduction bands. These intragrain VO structures can be treated as generation-recombination centers, which can convert various photoenergies (365–520 nm) into different current levels that form distinct surface potential levels; this is referred to as the photoelectric effect. PNF conductivity was enhanced 53.6-fold by enlarging the grain size (410 nm2) by increasing the annealing temperature, which can improve the photoelectric effect. In vitro removal of reactive oxygen species (ROS) can be achieved by using the photoelectric effect of PNFs. Also, the viability and shape of human bone marrow mesenchymal stem cells (hMSCs-BM) were also influenced significantly by the photobiomodulation effect. The cell damage and survival rate can be prevented and enhanced by using PNFs; metal oxide nanofibers are no longer only environmental sensors but can also be a bio-material to convert the photoenergy into bio-energy for biomedical science applications.
Abstract The nitrogenous nucleophile electrooxidation reaction (NOR) plays a vital role in the degradation and transformation of available nitrogen. Focusing on the NOR mediated by the β‐Ni(OH) 2 electrode, we decipher the transformation mechanism of the nitrogenous nucleophile. For the two‐step NOR, proton‐coupled electron transfer (PCET) is the bridge between electrocatalytic dehydrogenation from β‐Ni(OH) 2 to β‐Ni(OH)O, and the spontaneous nucleophile dehydrogenative oxidation reaction. This theory can give a good explanation for hydrazine and primary amine oxidation reactions, but is insufficient for the urea oxidation reaction (UOR). Through operando tracing of bond rupture and formation processes during the UOR, as well as theoretical calculations, we propose a possible UOR mechanism whereby intramolecular coupling of the N−N bond, accompanied by PCET, hydration and rearrangement processes, results in high performance and ca. 100 % N 2 selectivity. These discoveries clarify the evolution of nitrogenous molecules during the NOR, and they elucidate fundamental aspects of electrocatalysis involving nitrogen‐containing species.
It is notoriously difficult to distinguish the stoichiometric LiCoO2 (LCO) with a O3-I structure from its lithium defective O3-II phase because of their similar crystal symmetry. Interestingly, moreover, the O3-II phase shows metallic conductivity, whereas the O3-I phase is an electronic insulator. How to effectively reveal the intrinsic mechanism of the conductivity difference and nonequilibrium phase transition induced by the lithium deintercalation is of vital importance for its practical application and development. Based on the developed technology of in situ peak force tunneling atomic force microscopy (PF-TUNA) in liquids, the phase transition from O3-I to O3-II and consequent insulator-to-metal transition of LCO thin-film electrodes with preferred (003) orientation nanorods designed and prepared via magnetron sputtering were observed under an organic electrolyte for the first time in this work. Then, studying the post-mortem LCO thin-film electrode by using ex situ time-dependent XRD and conductive atomic force microscopy, we find the phase relaxation of LCO electrodes after the nonequilibrium deintercalation, further proving the differences of the electronic conductivity and work function between the O3-I and O3-II phases. Moreover, X-ray absorption spectroscopy results indicate that the oxidation of Co ions and the increasing of O 2p–Co 3d hybridization in the O3-II phase lead to electrical conductivity improvement in Li1–xCoO2. Simultaneously, it is found that the nonequilibrium deintercalation at a high charging rate can result in phase-transition hysteresis and the O3-I/O3-II coexistence at the charging end, which is explained well by an ionic blockade model with an antiphase boundary. At last, this work strongly suggests that PF-TUNA can be used to reveal the unconventional phenomena on the solid/liquid interfaces.
A simple, efficient, and cost-effective extended graphite as a supporting platform further supported the MnO2 growth for the construction of hierarchical flower-like MnO2/extended graphite. MnO2/extended graphite exhibited an increase in sp2 carbon bonds in comparison with that of extended graphite. It can be expected to display better electrical conductivity and further promote electron/ion transport kinetics for boosting the electrochemical performance in supercapacitors and glucose sensing. In supercapacitors, MnO2/extended graphite delivered an areal capacitance value of 20.4 mF cm-2 at 0.25 mA cm-2 current densities and great cycling stability (capacitance retention of 83% after 1000 cycles). In glucose sensing, MnO2/extended graphite exhibited a good linear relationship in glucose concentration up to about 5 mM, sensitivity of 43 μA mM-1cm-2, and the limit of detection of 0.081 mM. It is further concluded that MnO2/extended graphite could be a good candidate for the future design of synergistic multifunctional materials in electrochemical techniques.
Abstract Ion leaching from pure-phase oxygen-evolving electrocatalysts generally exists, leading to the collapse and loss of catalyst crystalline matrix. Here, different from previous design methodologies of pure-phase perovskites, we introduce soluble BaCl 2 and SrCl 2 into perovskites through a self-assembly process aimed at simultaneously tuning dual cation/anion leaching effects and optimizing ion match in perovskites to protect the crystalline matrix. As a proof-of-concept, self-assembled hybrid Ba 0.35 Sr 0.65 Co 0.8 Fe 0.2 O 3- δ (BSCF) nanocomposite (with BaCl 2 and SrCl 2 ) exhibits the low overpotential of 260 mV at 10 mA cm -2 in 0.1 M KOH. Multiple operando spectroscopic techniques reveal that the pre-leaching of soluble compounds lowers the difference of interfacial ion concentrations and thus endows the host phase in hybrid BSCF with abundant time and space to form stable edge/face-sharing surface structures. These self-optimized crystalline structures show stable lattice oxygen active sites and short reaction pathways between Co–Co/Fe metal active sites to trigger favorable adsorption of OH − species.
Metal-organic frameworks (MOFs) have been developed as an ideal platform for exploration of the relationship between intrinsic structure and catalytic activity, but the limited catalytic activity and stability has hampered their practical use in water splitting. Herein, we develop a bond length adjustment strategy for optimizing naphthalene-based MOFs that synthesized by acid etching Co-naphthalenedicarboxylic acid-based MOFs (donated as AE-CoNDA) to serve as efficient catalyst for water splitting. AE-CoNDA exhibits a low overpotential of 260 mV to reach 10 mA cm
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='rotate(60)'/%3e%3ccircle r='17' fill='%23000095'/%3e%3ccircle r='15' fill='%23fff'/%3e%3c/svg%3e)