Heterogeneous Electrocatalyst with Molecular Cobalt Ions Serving as the Center of Active Sites.

Molecular Co2+ ions were grafted onto doped graphene in a coordination environment, resulting in the formation of molecularly well-defined, highly active electrocatalytic sites at a heterogeneous interface for the oxygen evolution reaction (OER). The S dopants of graphene are suggested to be one of the binding sites and to be responsible for improving the intrinsic activity of the Co sites. The turnover frequency of such Co sites is greater than that of many Co-based nanostructures and IrO2 catalysts. Through a series of carefully designed experiments, the pathway for the evolution of the Co cation-based molecular catalyst for the OER was further demonstrated on such a single Co-ion site for the first time. The Co2+ ions were successively oxidized to Co3+ and Co4+ states prior to the OER. The sequential oxidation was coupled with the transfer of different numbers of protons/hydroxides and generated an active Co4+═O fragment. A side-on hydroperoxo ligand of the Co4+ site is proposed as a key intermediate for the formation of dioxygen.

Enzymatic-reaction induced production of polydopamine nanoparticles for sensitive and visual sensing of urea.

Dopamine (DA) has attracted extensive interest due to not only its important roles in physiological and pathological processes, but also its prospective applications in chemistry and materials science. In this work, we demonstrate that the urease catalytic reaction is an effective new approach for a better control of DA polymerization to polydopamine nanoparticles (PDA NPs). And we further develop an original and novel method for sensitive and visual sensing of urea through spectroscopic or particle size analysis. The detection is based on DA polymerization to PDA NPs that can be controlled by the reaction rate of urease-catalyzed urea hydrolysis, correspondingly, correlated with the varied urea concentration. The composition, morphologies and sizes of the resulting PDA NPs are characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and dynamic light scattering (DLS) spectroscopy, respectively. Under optimal reaction conditions, the UV absorbance of DA polymerization at 400 nm shows a good response towards urea detection over a range of 1 × 10(-7) to 1 × 10(-3) M with a limit of detection (LOD) of 100 nM (S/N = 3). Moreover, the sizes of the resulting PDA NPs increase linearly with urea concentration from 5 × 10(-6) to 1 × 10(-4) M. The newly developed assay allows the enzymatic-reaction driven PDA NPs to be used for quantitative detection of urea with many advantages, e.g. simple preparation, easy visualization, good sensitivity, wide detection range and low interference, in particular, no complex sensor-fabrication required.

Construction of Efficient 3D Gas Evolution Electrocatalyst for Hydrogen Evolution: Porous FeP Nanowire Arrays on Graphene Sheets.

A novel 3D hierarchical nanocomposite of vertically aligned porous FeP nano-wires on reduced graphene oxide is prepared as a demonstration of constructing an efficient hydrogen evolution catalyst. Extension of this nanostructuring strategy to other functional nanocomposites by combining different dimensional nanomaterials is attractive.

Improving mediated electron transport in anodic bioelectrocatalysis.

A novel design of a microbial fuel cell is realized by constructing bio-cocatalyst beads immobilized with riboflavin-secreting Escherichia coli and decoupling them from an anodic biocatalyst. A microbial fuel cell loaded with these bio-cocatalyst beads shows significantly enhanced performance without occupying an active electrode surface area.

A CO2-responsive surface with an amidine-terminated self-assembled monolayer for stimuli-induced selective adsorption.

A specific bifunctional molecule containing amidine is prepared to construct a CO2-responsive surface via molecular self-assembly. The smart surface undergoes CO2-responsive switching of surface charges and wettability, leading to distinctively selective adsorption of hydrophobic/hydrophilic molecules.

Strategies on the Design of Nitrogen-Doped Graphene.

Substitutional nitrogen doping in graphene has been a very powerful tool to tailor the pristine property of graphene and furthermore extend its application. While nitrogen-doped graphene (N-graphene) has shown many potential applications in catalysis, electronics, sensors and so on, there is still a lack of accurate control of substitutional nitrogen doping, and higher performance toward various applications is always needed. This Perspective summarizes the ongoing developments toward better control of nitrogen doping. Moreover, two recent strategies aiming to promote the activity of N-graphene are also discussed.