The CO₂-induced capillary blocking in anode flow field is one of the key adverse factors to reduce the performance of a micro-direct methanol fuel cell (μDMFC). In order to solve this problem, new polycarbonate (PC) flow field plates with nested arrangement of hydrophilic fuel channels and superhydrophobic gas channels were designed, fabricated, and tested in this work. The gas channels were treated with solvent-induced crystallization using acetone solution. The superhydrophobicity with 160° water contact angle and 2° tilting angle was obtained on the PC substrates. A dummy cell using hydrogen peroxide decomposition reaction and a test loop were separately set up to evaluate the flow fields’ performance. It was found that a 37 % pressure drop decrease can be obtained in the new serpentine flow field compared with that of the conventional one. The benefit of the new flow field to remove gas bubbles was also confirmed by an in situ visualization study on the dummy cell. Results show that the auxiliary superhydrophobic gas channels can speed up the discharge of the gas bubbles from the flow field, which will in turn improve the μDMFC performance.

Electrohydrodynamic jet (E-Jet) printing is a promising manufacturing technique for micro-/nano-patterned structures with high resolution, high efficiency and high material compatibility. However, further improvement of the necking ratio of the E-Jet is still limited by the focusing principle. Moreover, ink viscosity is limited to values well below 90 mPa s owing to the high probability of nozzle blockage. Here, we propose a microtip focused electrohydrodynamic jet (MFEJ) printing to overcome these limitations. This technique uses a solid microtip with a radius of curvature (ROC) of several micrometers rather than a hollow nozzle, which is very simple and highly efficient to prepare and can effectively avoid nozzle clogging problems even with high-viscosity printing ink. High-resolution patterns in diverse geometries were printed using different inks with a wide range of viscosities (8.4–3500 mPa s). Nanodroplets with an average diameter of 73 nm were achieved. Moreover, nanofibers with a diameter of 30 nm were obtained using a 4 μm ROC microtip and the necking ratio was as high as 266 : 1. To the best of our knowledge, this is the smallest droplet or fiber diameter directly obtained via E-Jet printing to date without further physical or chemical processing. This MFEJ printing technique can improve printing resolution at the nanoscale, significantly enlarge the material applicability and effectively avoid nozzle clogging for the fabrication of nanodevices.

This paper reports the use of electrohydrodynamic jet (E-jet) printing technique for producing a wide range of graphene micro-scale structures. Ethyl cellulose-dispersed graphene ink and Nafion-dispersed graphene ink were prepared and used for E-Jet printing. A glass slide and PDMS substrate were used for E-Jet printing of graphene ink. The E-jet printed graphene micro-scale structures using ethyl cellulose-dispersed graphene ink presented a feature of center arrayed graphene surrounded by the track of evaporated solution. However, the E-Jet printed graphene structures using Nafion-dispersed graphene ink exhibited uniform arranged features. It was observed that the resistivity of the graphene structures printed from the ethyl cellulose-dispersed graphene ink was much lower than that from the Nafion-dispersed graphene ink. In addition, the graphene micro-scale electrodes were E-Jet printed for preliminary electrochemical applications. The results showed that the graphene micro-scale electrodes had a distinct response for the lead ion. Furthermore, a Pt/graphene composite electrode was formed and an electrochemistry test was conducted. It was found that the Pt /graphene composite electrode had a more sensitive response compared with the pure Pt electrode for electrochemical sensing.