Vapor-fed microfluidic hydrogen generator

Abstract

Water-splitting devices that operate with humid air feeds are an attractive alternative for hydrogen production as the required water input can be obtained directly from ambient air. This article presents a novel proof-of-concept microfluidic platform that makes use of polymeric ion conductor (Nafion®) thin films to absorb water from air and performs the electrochemical water-splitting process. Modelling and experimental tools are used to demonstrate that these microstructured devices can achieve the delicate balance between water, gas, and ionic transport processes required for vapor-fed devices to operate continuously and at steady state, at current densities above 3 mA cm. The results presented here show that factors such as the thickness of the Nafion films covering the electrodes, convection of air streams, and water content of the ionomer can significantly affect the device performance. The insights presented in this work provide important guidelines for the material requirements and device designs that can be used to create practical electrochemical hydrogen generators that work directly under ambient air. Broader contextThe large scale deployment of hydrogen production technologies can be triggered by the development of electrolytic devices that function continuously under simple operation schemes. Water-splitting devices that operate under humid air are an attractive alternative to classic alkaline or proton exchange membrane electrolysis systems. In this regard, the implementation of water splitting technologies can be significantly simplified as the water feed could be obtained directly from the environment. Using polymeric ion-conducting materials in a microfluidic platform, this work balances the transport processes that are inherently limiting in devices operated with diluted water feeds, and demonstrates for the first time a vapor-fed microelectrolyzer capable of generating hydrogen at initial current densities above 10 mA cm −2

Photoelectrocatalytic Materials for Solar Water Splitting

“…The gaseous water is relatively easier split due to its lower standard Gibbs free energy of formation (−228.59 kJ mol −1 ) in comparison with that of liquid water (−237.18 kJ mol −1 ) . In 2015, Modestino has assessed the abilities of the vapor‐fed microfluidic electrolyzer in balancing the water, gas, and ionic transport processes during a continuous and steady water electrolysis . To support an efficient gas phase water splitting, the material should be hygroscopic to maintain a rapid and sufficient moisture adsorption, be porous to decrease the gas diffusion limitations, be highly ionic conductive and catalytically active for fast reaction kinetics.…”

Modeling, Simulation, and Implementation of Solar‐Driven Water‐Splitting Devices

“…[75] These dehydration effects have been recently demonstrated in a microfluidic water-vapor electrolyzer (Figure 4 d3). [76] As the device operated, the ohmic resistance increased because of the loss of water from the ionomer, which led to lower current densities at the steady state. Overall, water-vapor feeds are promising for solar-fuel generators, assuming that cost metrics and the correct current-density operating regime are amenable.…”

Mass transport aspects of electrochemical solar-hydrogen generation

“…When devices are operated with pure water or vapor, solid-state ion conductors are required to allow for ion-transport between the electrodes. 65,66 Under these circumstances the interfacial layer of the ionomer that covers the catalyst surface plays a very important role in defining the overall device performance. Mainly, this ionomer layer needs to allow for fast water, gas and ion transport between the surfaces of the catalyst into the bulk region of the device.…”

“…83 Notably, modelling of transport processes has provided insights into the design of solar-water splitting devices operated under water vapor feeds, 65,178,179 and near-neutral pH electrolytes. 43,82 These conditions have complex mass transport characteristics due to the limitations expected from the low concentration of water in vapor feeds, or the presence of multiple ionic species with non-uniform concentrations in buffered electrolytes.…”