An active micro-direct methanol fuel cell with self-circulation of fuel and built-in removal of CO2 bubbles

As an alternative or supplement to small batteries, the much-anticipated micro-direct methanol fuel cell ( DMFC) faces several key technical issues such as methanol crossover, reactant delivery, and byproduct release. This paper addresses two of the issues, removal of CO2 bubbles and delivery ofmethanol fuel, in a non-prohibitiveway for systemminiaturization. A recently reported bubble-driven pumpingmechanism is applied to develop active DMFCs free of an ancillary pump or a gas separator. The intrinsically generated CO2 bubbles in the anodicmicrochannels are used to pump and circulate the liquid fuel before being promptly removed as a part of the pumpingmechanism.Without a discrete liquid pump or gas separator, the widely known packaging penalty incurred within many micro-fuel-cell systems can be alleviated so that the system’s power/energy density does not decrease dramatically as a result of miniaturization. Since the power required for pumping is provided by the byproduct of the fuel cell reaction, the parasitic power loss due to an external pump is also eliminated. The fuel circulation is visually confirmed, and the effectiveness for fuel cell applications is verified during continuous operation of a DMFC for over 70minwith 1.2mL of 2Mmethanol. The same devicewas shown to operate for only 5min if the pumping mechanism is disabled by blocking the gas venting membrane. Methanol consumption while utilizing the reported self-circulation mechanism is estimated to be 46%. Different from common pump-free fuel delivery approaches, the reported mechanism delivers the fuel actively and is independent of gravity. © 2009 Elsevier B.V. All rights reserved.