Preparation Of Iridium-Based Catalysts And Study On The Performance Of Electrolyzed Water

Proton exchange membrane water electrolysis(PEMWE)hydrogen production technology is perfectly adapted to the volatility and intermittency of renewable energy sources like wind and light,making hydrogen an ideal carrier for renewable energy storage.The oxygen evolution reaction(OER)on the anode of the electrolyzer is regarded as the rate-limiting step of the water electrolysis due to its higher overpotential and sluggish reaction kinetics.Among the OER catalytic materials,only iridium(Ir)-based catalysts can balance the activity and durability well under strong acidity and high oxidation potentials,yet the scarcity and high cost of Ir metal limit its industrialization.Therefore,developing higher performance Ir-based catalysts and reducing the usage of Ir in electrolyzer are of great value for the wide application of PEMWE technology.In this paper,Ir-based catalysts with different particle sizes and support materials are prepared by oil bath and laser irradiation in liquids methods to investigate the relationship between the materials characteristic properties such as support type,Ir loading,Ir nanoparticles(Ir NPs)size,and the electrochemical properties as well as the membrane electrode assembly(MEA)performance of the catalysts.The main contents are as follows:(1)In this chapter,carbon black(XC-72)and titanium dioxide(TiO2)are selected as support materials to load Ir NPs for OER electrocatalysis.For the obtained 60 wt.%Ir/C and 60 wt.%Ir/TiO2,Ir NPs fully cover the surface of XC-72 and TiO2,and exhibit the same close average size of 1.6 nm.In rotating disk electrode(RDE)measurements,60 wt.%Ir/C and 60 wt.%Ir/TiO2 show the similar catalytic activity and reaction kinetics.In single cell testing,60 wt.%Ir/C and 60 wt.%Ir/TiO2 display nearly same excellent catalytic activities(<1.65-1.70 V@1 A/cm2;1.81～1.89 V@2 A/cm2).Besides,both of the catalysts remain stable for nearly 550 h without evident degradation at current density of 1.0 A/cm2 and 1.5 A/cm2.It is noteworthy that 60 wt.%Ir/C show a better durability than that of 60 wt.%Ir/TiO2 at 2.0 A/cm2.This can be attributed to the protection of internal carbon support by the abundant loading of Ir NPs.(2)Iridium-based catalysts 60 wt.%Ir/Ti3C2Tx,60 wt.%Ir/V4C3Tx and 60 wt.%Ir/Nb4C3Tx are prepared for OER electrocatalysis by loading Ir NPs on MXene materials:few-layer Ti3C2Tx,multilayer V4C3Tx and multilayer Nb4C3Tx,all of which are tightly covered by Ir NPs with a close average size of 1.70 nm.The RDE measurements show that 60 wt.%Ir/Ti3C2Tx exhibits the best catalytic activity(249 mV@10 mA/cm2)and reaction kinetics due to its larger electrochemcial active surface area(ECSA).In single cell testing,60 wt.%Ir/Ti3C2Tx remains stable for about 200 h without significant degradation at the current density of 1 A/cm2 and 1.5 A/cm2,which is significantly better than those of 60 wt.%Ir/V4C3Tx and 60 wt.%Ir/Nb4C3Tx.This can be attributed to the relatively stronger acid and oxidation resistance of the support Ti3C2Tx.(3)Using the technology of laser irradiation in liquid,large-size commercial iridium black particles dispersed in deionized water are irradiated by parallel light to be crushed by the fragmentation effect of the high-energy pulsed laser beam.The particle size distribution shows that the average size of Ir NPs decreases from the initial 6.00 nm to 1.20 nm,and the size distribution is more concentrated.Diffraction of x-rays(XRD)patterns show that the Ir NPs after irradiation have a better crystallinity.In RDE measurements,the small-sized Ir NPs show a higher catalytic activity and a better cycling stability.In single cell testing,the irradiated small-sized Ir NPs exhibit a lower voltage under the same current density,which proves that laser irradiation in liquid is an effective way to realize size control and to confer outstanding catalytic performance to metal NPs.