Gianmario Scotti

Remote detection NMR imaging of gas phase hydrogenation in microfluidic chips

The heterogeneous hydrogenation reaction of propene into propane in microreactors is studied by remote detection (RD) nuclear magnetic resonance (NMR). The reactors consist of 36 parallel microchannels (50 × 50 μm(2) cross sections) coated with a platinum catalyst. We show that RD NMR is capable of monitoring reactions with sub-millimeter spatial resolution over a field-of-view of 30 × 8 mm(2) with a steady-state time-of-flight time resolution in the tens of milliseconds range. The method enables the visualization of active zones in the reactors, and time-of-flight is used to image the flow velocity variations inside the reactor. The overall reaction yields determined by NMR varied from 10% to 50%, depending on the flow rate, temperature and length of the reaction channels. The reaction yield was highest for the channels with the lowest flow velocity. Propane T1 relaxation time in the channels, estimated by means of RD NMR images, was 270 ± 18 ms. No parahydrogen-induced polarization (PHIP) was observed in experiments carried out using parahydrogen-enriched H2, indicating fast spreading of the hydrogen atoms on the sputtered Pt surface. In spite of the low concentration of gases, RD NMR made imaging of gas phase hydrogenation of propene in microreactors feasible, and it is a highly versatile method for characterizing on-chip chemical reactions.

Integration of carbon felt gas diffusion layers in silicon micro fuel cells

We have integrated carbon felt, a traditional fuel cell gas diffusion layer, with silicon micro fuel cells. To this end we used two silicon microfabrication procedures using reactive ion etching: formation of black silicon and sinking of flowfield. The former decreases electrical contact resistance to the diffusion layer, the latter serves to contain the reactant gases. The micro fuel cells, where the flowfield was covered by black silicon nano-needles, showed better performance (127 mW cm−2) compared to the same cells without black silicon (114 mW cm−2). The black silicon fuel cells were also more stable during an overnight chronoamperometric measurement.

Lab-on-a-Chip Reactor Imaging with Unprecedented Chemical Resolution by Hadamard-Encoded Remote Detection NMR†

The development of microfluidic processes requires information-rich detection methods. Here we introduce the concept of remote detection exchange NMR spectroscopy (RD-EXSY), and show that, along with indirect spatial information extracted from time-of-flight data, it provides unique information about the active regions, reaction pathways, and intermediate products in a lab-on-a-chip reactor. Furthermore, we demonstrate that direct spatial resolution can be added to RD-EXSY efficiently by applying the principles of Hadamard spectroscopy.

Laser Direct Writing of Thick Hybrid Polymers for Microfluidic Chips

This work presents patterning of thick (10–50 µm) hybrid polymer structures of ORMOCER® by laser direct writing. ORMOCER® combine polymer-like fabrication processes with glass-like surface chemistry that is beneficial for many bio-microfluidic applications. ORMOCER® is liquid before exposure, so patterning is done by contact-free lithography, such as proximity exposure. With laser direct writing, we obtained higher resolution patterns, with smaller radius of curvature (~2–4 µm), compared to proximity exposure (~10–20 µm). Process parameters were studied to find the optimal dose for different exposure conditions and ORMOCER® layer thicknesses. Two fluidic devices were successfully fabricated: a directional wetting device (fluidic diode) and an electrophoresis chip. The fluidic diode chip operation depends on the sharp corner geometry and water contact angle, and both have been successfully tailored to obtain diodicity. Electrophoresis chips were used to separate of two fluorescent dyes, rhodamine 123 and fluorescein. The electrophoresis chip also made use of ORMOCER® to ORMOCER® bonding.

Bulk-Aluminum Microfabrication for Micro Fuel Cells

We present a simple method for microfabricating microfluidic devices by wet etching of bulk aluminum wafers. Aluminum wafers are identical to silicon wafers in terms of dimensions and can easily be processed in standard clean room processes like lithography, etching, and thin film deposition. Aluminum thin film wet etching in phosphoric acid-based etchants is well established. In this paper, it is extended to much greater depths than before. 80 μm deep structures have been fabricated. A hydrogen-fueled micro fuel cell has been microfabricated from bulk aluminum. These fuel cells achieved very high current densities of 1.1 A cm-2 and power density up to 228 mW cm-2. Considering the simplicity of bulk aluminum micromachining, these results are very encouraging.

Efficient Catalytic Microreactors with Atomic-Layer-Deposited Platinum Nanoparticles on Oxide Support

Microreactors attract a significant interest for chemical synthesis due to the benefits of small scales such as high surface to volume ratio, rapid thermal ramping, and well-understood laminar flows. The suitability of atomic layer deposition for application of both the nanoparticle catalyst and the support material on the surfaces of channels of microfabricated silicon microreactors is demonstrated in this research. Continuous-flow hydrogenation of propene into propane at low temperatures with TiO2 -supported catalytic Pt nanoparticles was used as a model reaction. Reaction yield and mass transport were monitored by high-sensitivity microcoil NMR spectroscopy as well as time-of-flight remote detection NMR imaging. The microreactors were shown to be very efficient in propene conversion into propane. The yield of 100 % was achieved at 50 °C with a reactor decorated with Pt nanoparticles of average size of roughly 1 nm and surface coverage of 3.2 % in 20 mm long reaction channels with a residence time of 1100 ms. The activity of the Pt catalyst surfaces was on the order of several to tens of mmol s-1  m-2 .

A micro heat exchanger microfabricated from bulk aluminium

We report a micro heat exchanger microfabricated from a bulk aluminium alloy substrate. The device is comprised of two 18 cm long microchannels, one on each side of an aluminium chip, capped on both sides with a thin self-adhesive polymer film. In spite of a cheap and facile fabrication method, initial experiments with the device show promising results. Area densities from 25000 m−1 to 45000 m−1 have been achieved. Compared to our previous work on aluminium microfluidic devices produced with a similar technology but from a different, less pure alloy, in this study the etched surfaces are significantly smoother, and present less photoresist delamination.

Symmetric silicon micro fuel cell with porous electrodes

We have developed a silicon microfabricted PEM fuel cell which uses hydrogen as fuel. The device employs flow channels with dual structure: isotropic plasma etching has been used for defining the large channels and gas conduits, and anisotropic plasma etching under passivating conditions (high concentration of oxygen in SF6) has been used to create silicon nanograss (black silicon) to increase surface area and triple junction points. The design presented here achieves the following goals: simple and cheap to fabricate, high power density (45mW/cm2), longevity and integrability.

Simple Stacking Methods for Silicon Micro Fuel Cells

Abstract: We present two simple methods, with parallel and serial gas flows, for the stacking of microfabricated silicon fuel cells with integrated current collectors, flow fields and gas diffusion layers. The gas diffusion layer is implemented using black silicon. In the two stacking methods proposed in this work, the fluidic apertures and gas flow topology are rotationally symmetric and enable us to stack fuel cells without an increase in the number of electrical or fluidic ports or interconnects. Thanks to this simplicity and the structural compactness of each cell, the obtained stacks are very thin (~1.6 mm for a two-cell stack). We have fabricated two-cell stacks with two different gas flow topologies and obtained an open-circuit voltage (OCV) of 1.6 V and a power density of 63 mW·cm −2 , proving the viability of the design. Keywords: silicon; micro fuel cell; stacking; deep reactive ion etching; polymer electrolyte membrane; black silicon 1. Introduction Fuel cells have been traditionally used for stationary power generation or in electrical vehicles, but miniaturized micro fuel cells (micro FC) have been, more recently, researched as a viable alternative to rechargeable batteries for applications, such as mobile phones, MP3 players, camcorders,