Bifunctional polymer interlayer promotes near infrared absorption organic photoanode for solar water oxidation

2022-07-13 0 By

Follow us as you like and subscribe for more updates first author: Tack Ho Lee Corresponding author: James R. Durrant Corresponding author: Imperial College London Paper DOI: full-text quick reference using polymer donor and small molecules of fullerenes receptor ontology (BHJs) heterojunction organic photovoltaic device show that the high performance, strong visible light and near infrared absorption, and low energy loss, is a strong candidate of solar-powered water decomposition.However, the poor stability of small molecule receptors underwater limits their viability.In this paper, we demonstrate a stable and efficient organic photoanode for water oxidation based on Y6:PM6 BHJ with another dual-function PM6 layer and Au/NiFe electrocatalyst top layer.The additional PM6 layer serves to 1) improve operational stability and 2) inhibit compound losses between the BHJ and electrocatalyst layer.Compared with anodes without PM6 layer, these BHJ/ PM6-based anodes have a photocurrent density of 4.0 mA cm-2 at 1.23 VRHE and have good operation stability, maintaining a photocurrent ≥2 mA cm-2 within 1 h.Experiments on solar water oxidation under near-infrared irradiation using these photoanodes show that the efficiency of incident photons to current is up to 25% at 770 nm.Developing new technologies for sustainable synthetic fuels and chemicals is a key challenge to achieve net zero carbon emissions.Photochemistry (PEC) Water decomposition has attracted a lot of attention as a potential low-cost, scalable pathway for solar-driven synthesis of green hydrogen, because solar to electricity and power to fuel conversion are integrated in a semiconductor/electrolyte system.So far, most PEC devices use inorganic semiconductor to absorb sunlight, but PEC devices based on organic semiconductor are attracting more and more attention.However, significant challenges remain in terms of performance, stability, energy level tunability, scalability and cost reduction.Organic semiconduction-based bulk heterojunction (BHJs) photovoltaic devices are a promising alternative to inorganic photovoltaic devices due to their bandgap tunability (through molecular engineering) and solution processability.The power conversion efficiency of organic photovoltaic (OPV) devices has increased rapidly in recent years, and now exceeds 18%.The development of non-fullerene-small molecule receptors (NF-SMAs) in particular has driven these efficiency improvements due to their long exciton diffusion lengths and energy level tunability (narrow band gaps, small energy shifts, etc.).However, the poor stability of typical organic BHJ in water limits its application in PEC water decomposition devices, especially because small molecules are easily dispersed or partially dissolved in aqueous solutions optimized for BHJ films, which is not the case for polymers.Based on this, wired photovoltaic cell concepts or complex packaging methods have been used to separate or protect SMA: polymer blends from aqueous solutions.In PEC cells, all-polymer BHJs improve the stability of organic photoelectrode by removing NF-SMAs from the blend.All-polymer photopoles for water reduction have shown promising photocurrents of up to 8 mA cm-2, whereas photoanodes for the more thermodynamically and kinetically challenging water oxidation reactions are limited to about 2 mA cm-2.Improving the performance of organic photoanodes is still the main challenge to realize the water decomposition of whole PEC using tandem organic photoanode and photoanode.Another challenge is that the all-polymer photopoles and photoanodes reported to date are mainly limited to overlapping visible light absorption, which limits their application in organic PEC series devices.Therefore, the development of high-performance organic photoanodes, especially near-infrared absorption organic photoanodes, which can make full use of the solar spectrum through complementary absorption with all-polymer photocathode, is a key challenge.In this paper, we report a near-infrared photoanode for solar water oxidation based on polymer donor and NF-SMA BHJs.After BHJ deposition, a polymer coating is deposited in water using a thin-film transfer process. The polymer coating has the dual function of protecting the BHJ from aqueous electrolyte and preventing photogenerated electrons from returning to the anode/electrolyte interface.The resulting dual-functional polymer sandwich photoanode structure shows significant water oxidation performance and operational stability, which is much better than the previously reported organic photoanode.FIG. 1 A) Molecular structures of PM6 and Y6.B) PM6 membrane transfer from water to Y6: schematic diagram and corresponding photos of PM6 membrane.C) Absorption spectra of Y6:PM6 film with PM6 coating (denoised as Y6:PM6/PM6) and Y6:PM6 film.D) Schematic diagram of organic photoanode device structure.FIG. 2 a) LSV scanning of y6:PM6 /PM6 and Y6:PM6 photoanodes in 0.1 M KOH solution (pH 13) under intermittent 1 sunlight.B) Normalized timing current curve under 1 sunlight in 0.1 M KOH solution (pH 13) at 1.23 VRHE.The digital photograph in the inset shows oxygen release from the surface of the Y6:PM6/PM6 photoanode during measurement.C) IPCE spectra of Y6:PM6/PM6 photoanode in 0.1 M KOH solution (pH 13) at 1.23 VRHE.D) Timing current curve (at 1.23VRHE) of Y6:PM6/PM6 photoanode in 1 M borate electrolyte (buffer pH 8.1), 0.1 M KOH solution (pH 13) and 1 M KOH solution (pH 14) under 1 continuous sunshine.FIG.3 a) Negative current response of 0.5~1.3VRHE after lights out.B) The amount of negative charge, as a function of applied bias, is obtained by integrating the negative transient current.C) Y6:PM6/PM6 photoanode and d) Y6:PM6 photoanode energy level diagram.The PM6 layer prevents the reverse electron transfer of Y6:PM6 BHJ.In summary, in this paper, by introducing polymer interlayer between BHJ and electrolyte, the efficient near infrared absorption of Y6:PM6 organic BHJ can be used as an organic photoanode for direct solar driven water oxidation.Organic light absorbents for water decomposition are limited to polymer semiconductors due to the poor underwater stability of small molecules or the large amount of packaging required.The simple transfer of the hydrophobic polymer layer to water significantly improves the operational stability of organic photoanodes, which provides a wide range of options for organic semiconductors in underwater applications.In addition, ZnO nanoparticles as the substrate of the organic film improve the stability, and the selection of OER catalyst chemical deposition method can avoid the destruction of the organic film in the photoanode preparation process.After optimization of ITO/ZnO/Y6: PM6 / PM6 / Au/NiFeOOH light anode under 1.23 VRHE obtained significant Jph mA (4 cm – 2), in the pH for 13 consecutive sun Jph mA cm – 2 or more stability increased significantly, up to the 4000 s.At pH 8.1 and under the same operating conditions, water oxidation provides unprecedented operational stability after prolonged storage in ambient air.In addition, the PM6 layer acts as an effective electron barrier, reducing the initial potential to about 400 mV by inhibiting unexpected charge recombination at the anode/electrolyte interface.The stability and high performance of solution treated organic photoanodes with broadband absorption up to 900 nm suggest that dual-functional polymer interlayers enhance the possibility of producing solar-driven fuels from PEC cells based on economical and scalable organic semiconductors.