Observation of Photovoltaic Action from Photoacid-Modified Nafion Due to Light-Driven Ion Transport

Abstract

Replacing passive ion-exchange membranes, like Nafion, with membranes that use light to drive ion transport would allow membranes in photoelectrochemical technologies to serve in an active role. Toward this, we modified perfluorosulfonic acid ionomer membranes with organic pyrenol-based photoacid dyes to sensitize the membranes to visible light and initiate proton transport. Covalent modification of the membranes was achieved by reacting Nafion sulfonyl fluoride poly-(perfluorosulfonyl fluoride) membranes with the photoacid 8-hydroxypyrene-1,3,6-tris(2-aminoethylsulfonamide). The modified membranes were strongly colored and maintained a high selectivity for cations over anions. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and ionexchange measurements together provided strong evidence of covalent bond formation between the photoacids and the polymer membranes. Visible-light illumination of the photoacid-modified membranes resulted in a maximum power-producing ionic photoresponse of ∼100 μA/cm 2 and ∼1 mV under 40 Suns equivalent excitation with 405 nm light. In comparison, membranes that did not contain photoacids and instead contained ionically associated Ru II −polypyridyl coordination compound dyes, which are not photoacids, exhibited little-to-no photoeffects (∼1 μA/cm 2 ). These disparate photocurrents, yet similar yields for nonradiative excited-state decay from the photoacids and the Ru II dyes, suggest temperature gradients were not likely the cause of the observed photovoltaic action from photoacid-modified membranes. Moreover, spectral response measurements supported that light absorption by the covalently bound photoacids was required in order to observe photoeffects. These results represent the first demonstration of photovoltaic action from an ion-exchange membrane and offer promise for supplementing the power demands of electrochemical processes with renewable sunlight-driven ion transport.

Syntheses of Exceptionally Stable Aluminum(III) Metal–Organic Frameworks: How to Grow High‐Quality, Large, Single Crystals

“…The current increases upon irradiation at shorter wavelength, which is consistent with the higher light absorbances of AlTCS‐1 and ‐2 at shorter wavelength, relative to those at longer wavelength. A similar phenomenon was also reported by Ardo et al . The generated photocurrent increases with increasing applied bias potential.…”

“…[29] The current increases upon irradiation at shorter wavelength, whichi sc onsistent with the higher light absorbances of AlTCS-1 and -2 at shorter wavelength,r elative to those at longerw avelength. As imilarp henomenon was also reported by Ardo et al [30] The generated photocurrent increases with increasing applied bias potential. Such phenomena of other materials were also observed by Zhang et al [31] Undert he illumination of 385 nm light, the photocurrent densities of AlTCS-1a nd -2 reach 100 and 60 nA cm À2 ,r espectively, at 0.6 V( vs. Ag/AgCl).…”

Highly Efficient Ionic Photocurrent Generation through WS2‐Based 2D Nanofluidic Channels

“…So far, nanofluidic ion transport in existing membrane materials follows the direction of their concentration gradient, and mostly exhibits symmetric transport behaviors . Recently, using the energy of light, establishing a chemical gradient by active transport of ionic species across a synthetic membrane without the assistance of any biological components attracts broad research interest . For example, recently, we discovered a coupled photon–electron–ion transport mode in 2D nanofluidic systems that asymmetric light irradiation on a graphene oxide strip initiates a transmembrane ionic flow, following a diffusion‐based charge separation mechanism .…”

Ion Transport in Nanofluidic Devices for Energy Harvesting

“…The light irradiation will change the surface charge of the membrane 99,115 or drive a charge gradient of photo-responsive molecules. 96,116,117 These artificial photo-driven ion pumps are similar to the natural ion pumps in bacteriorhodopsin.…”