Kevin Kaufmann

Highly ordered multilayered 3D graphene decorated with metal nanoparticles

Highly ordered multi-layered three-dimensional (3D) graphene structures decorated with Pd, Pt and Au metal nanoparticles are prepared and characterized. The ability to control the morphology, distribution and size of the metal nanoparticles on the 3D graphene support upon changing the electro- and electroless-deposition conditions is demonstrated. Tailor-made Pt nanostructures, with nanospike and nanoparticle shapes, are prepared using electroless deposition techniques. Au nanoflowers and nanoparticle structures and Pd nanocubes are obtained following electrodeposition onto the 3D graphene support. The deposition patterns and trends are characterized. The greatly enhanced electrocatalytic activity of the metal-NP–graphene surfaces has been illustrated in connection to voltammetric measurements of ORR and hydrogen peroxide at 3D-graphene coated with Pt and Pd nanoparticles, respectively. Such metal nanoparticles decorated multi-layer 3D graphene allows for high mass transport access and catalytic activity for a diverse range of applications, including sensor and fuel-cell technologies.

Fully loaded micromotors for combinatorial delivery and autonomous release of cargoes

Integrating functional self-propelled Zinc micromotors are created by coup-ling electrodeposition with hard dual-templating synthesis. The micromotors concurrently possess four robust functions including a remarkably high loading capacity, combinatorial delivery of cargoes, autonomous release of encapsulated payloads, and self-destruction. This concept could be expanded to simultaneous encapsulation of various payloads for different functionalities such as therapy, diagnostics, and imaging.

Micromotor-Based Energy Generation†

A micromotor-based strategy for energy generation, utilizing the conversion of liquid-phase hydrogen to usable hydrogen gas (H2), is described. The new motion-based H2-generation concept relies on the movement of Pt-black/Ti Janus microparticle motors in a solution of sodium borohydride (NaBH4) fuel. This is the first report of using NaBH4 for powering micromotors. The autonomous motion of these catalytic micromotors, as well as their bubble generation, leads to enhanced mixing and transport of NaBH4 towards the Pt-black catalytic surface (compared to static microparticles or films), and hence to a substantially faster rate of H2 production. The practical utility of these micromotors is illustrated by powering a hydrogen-oxygen fuel cell car by an on-board motion-based hydrogen and oxygen generation. The new micromotor approach paves the way for the development of efficient on-site energy generation for powering external devices or meeting growing demands on the energy grid.

Tunable hierarchical macro/mesoporous gold microwires fabricated by dual-templating and dealloying processes

Tailor-made highly ordered macro/mesoporous hierarchical metal architectures have been created by combining sphere lithography, membrane template electrodeposition and alloy-etching processes. The new double-template preparation route involves the electrodeposition of Au/Ag alloy within the interstitial (void) spaces of polystyrene (PS) microspheres which are closely packed within the micropores of a polycarbonate membrane (PC), followed by dealloying of the Ag component and dissolution of the microsphere and membrane templates. The net results of combining such sphere lithography and silver etching is the creation of highly regular three-dimensional macro/mesoporous gold architecture with well-controlled sizes and shapes. The morphology and porosity of the new hierarchical porous structures can be tailored by controlling the preparation conditions, such as the composition of the metal mixture plating solution, the size of the microspheres template, or the dealloying time. Such tunable macro/mesoporous hierarchical structures offer control of the electrochemical reactivity and of the fuel mass transport, as illustrated for the enhanced oxygen reduction reaction (ORR) and hydrogen-peroxide detection. The new double templated electrodeposition method provides an attractive route for preparing highly controllable multiscale porous materials and diverse morphologies based on different materials and hence holds considerable promise for designing electrocatalytic or bioelectrocatalytic surfaces for a variety sensing and energy applications.

Micromotor-Based Biomimetic Carbon Dioxide Sequestration: Towards Mobile Microscrubbers.

We describe a mobile CO2 scrubbing platform that offers a greatly accelerated biomimetic sequestration based on a self-propelled carbonic anhydrase (CA) functionalized micromotor. The CO2 hydration capability of CA is coupled with the rapid movement of catalytic micromotors, and along with the corresponding fluid dynamics, results in a highly efficient mobile CO2 scrubbing microsystem. The continuous movement of CA and enhanced mass transport of the CO2 substrate lead to significant improvements in the sequestration efficiency and speed over stationary immobilized or free CA platforms. This system is a promising approach to rapid and enhanced CO2 sequestration platforms for addressing growing concerns over the buildup of greenhouse gas.

Dual-enzyme natural motors incorporating decontamination and propulsion capabilities

Self-propelled dual-function biocatalytic motors, consisting of unmodified natural tissue and capable of in-motion bioremediation, are described. These enzyme-rich tissue motors rely on the catalase and peroxidase activities of their Raphanus sativus radish body for their propulsion and remediation actions, respectively. The continuous movement of the biocatalytic tissue motors through the contaminated sample facilitates the dynamic removal of phenolic pollutants. Hydrogen peroxide plays a dual role in the propulsion and decontamination processes, as the motor fuel and as co-substrate for the phenol transformation, respectively. Localized fluid transport and mixing, associated with the movement of the radish motors and corresponding generation of microbubbles, greatly improve the remediation efficiency resulting in maximal removal of pollutants within 3 min. The new ‘on-the-fly’ remediation process is cost effective as it obviates the need for expensive isolated enzymes and relies on environmental-friendly plant tissues.

Self-propelled chemically-powered plant-tissue biomotors

Self-propelled biocatalytic motors based on plant tissues are described. The tissue motors rely on their rich catalase activity towards biocatalytic decomposition of the H2O2 fuel and generation of the bubble thrust. These biomotors obviate the need for pure enzymes, and offer a remarkably low cost, good lifetime and thermostability.

Improved oxygen reduction reaction activities with amino acid R group functionalized PEG at platinum surfaces

We demonstrate here that coupling specific amino acid “R” groups to polyethylene glycol (PEG) chains through amide bonds and adsorbing them to platinum (Pt) black improves oxygen reduction reaction (ORR) catalysis over a bare metal, even at high polymer loadings. Through our studies, we first show that the presence of PEG on the Pt nanoparticles increases half-wave (E1/2) potentials, most likely by preventing Pt oxidation or Pt–OH formation. We also show, however, that increases in E1/2 did not necessarily correlate with gains in mass activities, and that while commercial PEG–OH in fact lowered mass activities, conjugation of PEG to alcohol-containing amino acid R groups connected by amide bonds led to 100–200% gains in reactivity. This work presents evidence that counters the common conception that organic capping ligands decrease catalytic activity; in fact activity may actually be improved over the bare metal through judicious choice and design of ligands that inhibit Pt oxidation and control chain packing at the Pt surface. These studies therefore show that it may still be possible to have ligands on a nanoparticle surface that allow the particles to be well-dispersed on an electrode surface while simultaneously enhancing catalysis without further particle treatment.