Abstract:
Membrane-less microfluidic reactors for water electrolysis can serve as a disruptive technology for the sustainable production of hydrogen utilizing excess electricity from intermittent renewable energy sources. Membrane-less electrolyzers facilitate flexible pH operation of electrolyzers using liquid electrolytes, which have higher ionic conductivity than solid membranes. Herein, we demonstrate a microfluidic electrolyzer driven by electrochemical neutralization energy in which an asymmetric electrolyte configuration (acidic catholyte and alkaline anolyte) was used for the first time to reduce the voltage requirement of water electrolysis drastically. The potential recorded for water electrolysis in this device was 1.3 V for an asymmetric electrolyte, 1.96 V for an acidic electrolyte, and 1.94 V for an alkaline electrolyte. The product gas separation was attained by balancing inertial and viscous forces acting on the fluid induced by the flow of electrolyte. The flow in the microchannel was characterized by a low Reynolds number (43.94) and high Peclet number (7.29 x 10(3) and 1.75 x 10(4) for H-2 and O-2, respectively), which implies a highly viscous flow and negligible diffusion of gas products across the electrodes. The charge transfer resistance for water electrolysis with an asymmetric electrolyte was less (47.2 omega cm(2)) as compared to acidic (272.94 omega cm(2)) and alkaline electrolytes (292.92 omega cm(2)). The reactor exhibits 4 hours of stability with no perturbation in current density at a 1.4 ml min(-1) electrolyte flow rate. The product crossover analyzed by gas chromatography was less than 5% with H-2 and O-2 volumetric collection efficiencies of 93.14% and 91.43%, respectively. The device has a performance efficiency of 96.5% based on a 150 mu m interelectrode distance.