Polypyrrole Serving as Multifunctional Surface Modifier for Photoanode Enables Efficient Photoelectrochemical Water...

Conjugated polymer polypyrrole (PPy) with high electrical conductivity and excellent photothermal effect has been adopted as multifunctional surface modifier on ternary metal sulfide (CdIn₂ S₄ , CIS) photoanode for photoelectrochemical (PEC) water splitting for the first time. As a p-type conducting polymer, PPy forms p-n junction with n-type CIS to relieve the bulk carrier recombination. Besides, the incorporation of Ni ions into PPy matrix further enhances the surface charge carrier transfer at photoanode/electrolyte interfaces. Furthermore, the excellent photothermal effect of PPy produces heat under near-infrared (NIR) irradiation, which can elevate the temperature of CIS photoanode in situ and further enhance the PEC performance. As a result, the optimum CIS/Ni-PPy photoanode shows an obviously enhanced photocurrent density of 6.07 mA cm^-2 at 1.23 V versus reversible hydrogen electrode under the irradiation of AM 1.5G combined with NIR light, which is the highest among all the CIS based photoanodes reported to date. The synergetic effect of Ni-PPy significantly suppresses the bulk recombination, decreases the carrier transfer resistance, and accelerates the surface water oxidation dynamics, resulting in high carrier injection efficiency over 80% in the measured potential range. The universality of the multifunctional surface modifier strategy has also been confirmed on metal oxide photoanode.