Proton exchange membrane electrolysis sustained by water vapor

Abstract

The current-voltage characteristics of a proton exchange membrane (PEM) electrolyzer constructed with an IrRuO x water oxidation catalyst and a Pt black water reduction catalyst, under operation with water vapor from a humidified carrier gas, have been investigated as a function of the gas flow rate, the relative humidity, and the presence of oxygen. The performance of the system with water vapor was also compared to the performance when the device was immersed in liquid water. With a humidified Ar(g) input stream at 20C, an electrolysis current density of 10 mA cm À2 was sustained at an applied voltage of $1.6 V, with a current density of 20 mA cm À2 observed at $1.7 V. In the system evaluated, at current densities >40 mA cm À2 the electrolysis of water vapor was limited by the mass flux of water to the PEM. At <40 mA cm À2 , the electrolysis of water vapor supported a given current density at a lower applied bias than did the electrolysis of liquid water. The relative humidity of the input carrier gas strongly affected the current-voltage behavior, with lower electrolysis current density attributed to dehydration of the PEM at reduced humidity values. The results provide a proof-of-concept that, with sufficiently active catalysts, an efficient solar photoelectrolyzer could be operated only with water vapor as the feedstock, even at the low operating temperatures that may result in the absence of active heating. This approach therefore offers a route to avoid the light attenuation and mass transport limitations that are associated with bubble formation in these systems.

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

“…[35b] The electrolysis of water using commercially available membrane-electrode assemblies with a water-vapor feed has demonstrated operating current densities on the order of tens of mA cm À2 , which is sufficient for the operation of a broad range of solar-driven water-splitting devices. [73] Reduced current density and cell failure using vapor feed are often caused by limitations in the mass transport of the reactant water and dehydration of the membrane electrolyte resulting in increased ohmic losses. A light-driven demonstration system was reported that used a membrane-electrode assembly with photoactive TiO 2 nanoparticles incorporated into the membrane layer (Figure 4 d1).…”

Solar Hydrogen Reaching Maturity

“…They noted the important effect of relative humidity on performance, whereas absolute humidity has less importance. Spurgeon and Lewis showed that a vapor phase electrolyzer can reach a current density of 20 mA cm À2 , congruent with current densities of PV and PEC devices, but found that performance dropped steeply at reduced relative humidity [21]. Their work suggests that ion exchange membranes can be operated in vapor phase, albeit at lower current densities than usually encountered in electrolyzers.…”

“…Although water concentration in air is rather low, the moderate current density encountered in solar H 2 devices implies they should be able to extract sufficient water from it. Some authors have suggested the use of air as a water feedstock recently [21,68,69]. They noted the important effect of relative humidity on performance, whereas absolute humidity has less importance.…”

“…The best choice for the electrolyzer is a Polymer Electrolyte Membrane (PEM) electrolyzer, since this type can more easily handle fluctuating input currents [20]. It can be scaled much smaller than the PV modules, since sunshine is diffuse (100 mW cm À2 , corresponding to maximal photocurrents around 20-30 mA cm À2 ) and electrolyzers economically operate at high current densities of >1 A cm À2 [21].…”

An Integrated Device View on Photo-Electrochemical Solar-Hydrogen Generation

“…These devices are in the early stage of development, but guidelines for their fabrications have been drawn from modeling studies (58,115), and experimental operation of MEA electrolyzers on the vapor phase has been demonstrated (116). Also, proper thermal management in devices can allow systems to operate continuously at higher levels of efficiency.…”