An on-demand microfluidic hydrogen generator with self-regulated gas generation and self-circulated reactant exchange with a rechargeable reservoir

Abstract

This article introduces an on-demand microfluidic hydrogen generator that can be integrated with a microproton exchange membrane (PEM) fuel cell. The catalytic reaction, reactant circulation, gas/liquid separation, and autonomous control functionalities are all integrated into a single microfluidic device. It generates hydrated hydrogen gas from an aqueous ammonia borane solution which is circulated and exchanged between the microfluidic reactor and a rechargeable fuel reservoir without any parasitic power consumption. Ammonia borane is chosen instead of sodium borohydride because of its faster hydrogen generation rate, higher hydrogen storage capability, stability, and better catalyst durability. The self-circulation of the ammonia borane solution was achieved using directional growth and selective venting of hydrogen bubbles in micro-channels, which leads to agitation and addition of fresh solution without consumption of electrical power. The self-regulation mechanism ensures that hydrogen can be supplied to a fuel cell according to the exact demand of the current output of the fuel cell. The circulation flow rate of ammonia borane solution is also automatically regulated by the venting rate of hydrogen at the gas outlet. Design, fabrication, and testing results of a prototype system are described. The hydrogen generator is capable of generating hydrogen gas at a maximum rate of 0.6 ml/min (2.1 ml/min cm 2 ) and circulating aqueous ammonia borane at a maximum flow rate of *15.7 ll/min. The device has also been connected with a micro-PEM fuel cell to demonstrate the feasibility of its practical applications in a high-impedance system.

Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors

“…150 Similarly for the case of a hydrogen generator, self-circulation of electrolyte can be implemented to promote directional growth and selective venting of hydrogen bubbles in micro-channels, causing flow mix and fresh solution incoming without extra power required. 151 When coupled with a fuel cell, such mechanism ensures that hydrogen is supplied as demanded by its consumption rate in a fuel cell.…”

Spatial and temporal scaling of unequal microbubble coalescence

“…In the environmental industry, the most common application of microbubbles is in the water and waste-water treatment [9][10][11][12][13] . Important micro/nano bubble technologies involved in lab-on-a-chip 14,15 , airlift bioreactor 16,17 , fluorinations 18 , hydrogenation 19,20 and DNA analysis 21 are attracting more and more attention. Bubble coalescence is a common phenomenon in different types of applications as the surface areas when bubbles are in touch tend to minimize.…”

Electronic desalting for controlling the ionic environment in droplet-based biosensing platforms

“…The desalting capacity also increased for the test electrodes with the area enhancement, and we measured this within micro-droplets at various desalting voltages. Although the physical area was dramatically enhanced (Figure 3(b)) and expected to provide two orders of magnitude improvement, 22 we only observed a limited increase during experiments. This may be attributed to either the incomplete coverage of the surface in contact with the droplet because of the increased surface energy cost of nanostructured surfaces that typically renders them repellant, or exclusion effects from steric issues that possibly come into play for ion absorption over a non-ideal surface as the roughness ( 50 nm) approaches the phenomenological lengthscale, k D .…”

“…High surface area (HSA) platinum-black electrodes were prepared by electrodeposition methods, 21,22 using a Gamry Reference 600 Potentiostat (Gamry Instruments, PA, USA). Pt-black was galvanostatically deposited on a seed layer of 1000 Å thick Ti/Pt from dihydrogen hexachloroplatinate (0.08 mM H 2 PtCl 6 Á6H 2 O, Sigma Aldrich, with 0.25 g/L of (CH 3 COO) 2 Pb, Alfa Aesar) at À0.08 A/cm 2 vs. Ag/AgCl.…”