Confinement Catalyst of Co9S8@N-Doped Carbon Derived from Intercalated Co(OH)2 Precursor and Enhanced Electrocatalytic Oxygen Reduction Performance.

Oxygen reduction reaction (ORR) is an important cathode reaction in fuel cells and metal-air batteries. Composites of transition-metal sulfides (TMSs) and nitrogen-doped carbon (NC) are promising alternative ORR catalysts because of their high catalytic activity. However, the agglomeration of TMS particles limits practical applications. Here, a confinement catalyst composed of Co9S8@NC with a flower-like morphology was derived from metanilic intercalated Co(OH)2 through interlayer-confined carbonation accompanied with host-layer sulfidation. The surface of the Co9S8 particles is covered with a few layers of nitrogen-doped graphene, which can prevent the Co9S8 particles from agglomeration and also produce catalytic activity affected by internal Co9S8. Thus, the Co9S8@NC material achieves excellent ORR performance with a half-wave potential of 0.861 VRHE. In addition, an oxide layer on the surface of Co9S8@NC is fabricated shortly after the ORR starts. Further tests and density functional theory calculations indicated that this cobalt oxide layer can increase the electrochemically active area of Co9S8@NC as well as reduce the ORR energy barrier, thereby providing more catalytic active sites and enhancing the intrinsic catalytic activity, thus achieving a self-activation effect during the electrochemical reaction process.

Peptide-Programmable Nanoparticle Superstructures with Tailored Electrocatalytic Activity.

Biomaterials derived via programmable supramolecular protein assembly provide a viable means of constructing precisely defined structures. Here, we present programmed superstructures of AuPt nanoparticles (NPs) on carbon nanotubes (CNTs) that exhibit distinct electrocatalytic activities with respect to the nanoparticle positions via rationally modulated peptide-mediated assembly. De novo designed peptides assemble into six-helix bundles along the CNT axis to form a suprahelical structure. Surface cysteine residues of the peptides create AuPt-specific nucleation site, which allow for precise positioning of NPs onto helical geometries, as confirmed by 3-D reconstruction using electron tomography. The electrocatalytic model system, i.e., AuPt for oxygen reduction, yields electrochemical response signals that reflect the controlled arrangement of NPs in the intended assemblies. Our design approach can be expanded to versatile fields to build sophisticated functional assemblies.

Sol-gel Synthesis, Photo- and Electrocatalytic Properties of Mesoporous TiO2 Modified with Transition Metal Ions.

Mesoporous nanosized titania films modified with Co2+, Ni2+, Mn3+, and Cu2+ ions have been produced by templated sol-gel method and characterized by optical spectroscopy, X-ray diffraction (XRD), and Brunauer, Emmett, and Teller (BET) surface area measurement. Band gap energy and the position of flat band potentials were estimated by photoelectrochemical measurements. The films doped with transition metals possessed higher photocurrent quantum yield, as well as photo- and electrochemical activity compared to undoped samples. Mn+/TiO2 (M-Co, Ni, Mn, Cu) electrodes with low dopant content demonstrate high efficiency in electrocatalytic reduction of dissolved oxygen. Polarization curves of TiO2, TiO2/Ni2+, TiO2/Co2+/3+, and TiO2/Mn3+ electrodes contain only one current wave (oxygen reduction current). It means that reaction proceeds without the formation of an intermediate product H2O2.

Promoting the Electrochemical Performances by Chemical Depositing of Gold Nanoparticles Inside Pores of 3D Nitrogen-Doped Carbon Nanocages.

Carbon Nanomaterials are excellent electrode materials due to their extraordinary conductivity, prolific structures, and morphologies. Herein, a novel nanocarbon-based material (Au@NCNC) was synthesized by embedding gold nanoparticles (AuNPs) inside the pores of three-dimensional hierarchical nitrogen-doped carbon nanocages (NCNC) through an in situ chemical deposition method. The resultant Au@NCNC was employed as an electrochemical catalyst for the oxygen reduction reaction (ORR) and as an electrode material for supercapacitors. The conductivity and hydrophilicity of Au@NCNC were much more improved than those of pristine NCNC. Meanwhile, the bubble adhesive force on the Au@NCNC film was much lower underwater than that of NCNC, which provided easy accessibility to the active sites of reactants, such as hydrated O2. Therefore, the deposition of AuNPs inside pores of NCNC facilitated the transfer of electrons and diffusion of ions, promoting the electrocatalytic performance of Au@NCNC. As a result, Au@NCNC exhibited high performance toward ORR, which manifested in high numbers of electron transfer (3.7-3.9), high kinetic current density, enhanced electrocatalytic stability, and remarkable methanol durability. Moreover, Au@NCNC displayed high specific capacitance, good rate capability, and cycling stability with ∼97% of its initial capacitance retained at the high current density of 10 A g-1 after 5000 cycles. This could be attributed to the synergetic effect of ultrafine gold nanoparticles, the hierarchical porous structure, and the hydrophilic surface of NCNC as well. This work offers an excellent alternative for Pt-based catalysts in fuel cells, ORR, and supercapacitive electrode materials by enhancing the conductivity and surface hydrophilicity of electrocatalysts.

Three toxic gases meet in the mitochondria.

The rationale of the study was two-fold: (i) develop a functional synthetic model of the Cytochrome c oxidase (CcO) active site, (ii) use it as a convenient tool to understand or predict the outcome of the reaction of CcO with ligands (physiologically relevant gases and other ligands). At physiological pH and potential, the model catalyzes the 4-electron reduction of oxygen. This model was immobilized on self-assembled-monolayer (SAM) modified electrode. During catalytic oxygen reduction, electron delivery through SAMs is rate limiting, similar to the situation in CcO. This model contains all three redox-active components in CcO's active site, which are required to minimize the production of partially-reduced-oxygen-species (PROS): Fe-heme ("heme a3") in a myoglobin-like model fitted with a proximal imidazole ligand, and a distal tris-imidazole Copper ("CuB") complex, where one imidazole is cross-linked to a phenol (mimicking "Tyr244"). This functional CcO model demonstrates how CcO itself might tolerate the hormone NO (which diffuses through the mitochondria). It is proposed that CuB delivers superoxide to NO bound to Fe-heme forming peroxynitrite, then nitrate that diffuses away. Another toxic gas, H2S, has exceptional biological effects: at ~80 ppm, H2S induces a state similar to hibernation in mice, lowering the animal's temperature and slowing respiration. Using our functional CcO model, we have demonstrated that at the same concentration range H2S can reversibly inhibit catalytic oxygen reduction. Such a reversible catalytic process on the model was also demonstrated with an organic compound, tetrazole (TZ). Following studies showed that TZ reversibly inhibits respiration in isolated mitochondria, and induces deactivation of platelets, a mitochondria-rich key component of blood coagulation. Hence, this program is a rare example illustrating the use of a functional model to understand and predict physiologically important reactions at the active site of CcO.