Flexible electrodes, particularly paper electrodes modified with polypyrrole, have shown promise in energy-related applications. We have earlier demonstrated the usage of paper electrodes modified with polypyrrole as a flexible and suitable photoanode for photoelectrochemical water splitting (PEC). Further, modification of this electrode system with an appropriate tandem absorber system for solar fuel production is interesting in developing efficient photoanodes. In this study, we study the PEC performance of flexible polypyrrole-based paper photoanodes (PPy-PAs) by decorating them with rGO@Cu2Zn- SnS4 chalcopyrites (rGO@CZTS/PPy-PAs). The lower bandgap (~ 1.5 eV) of the rGO@CZTS/PPy-PAs system allows for efficient visible light absorption, substantially improving PEC water-splitting reactions. The rGO@CZTS/PPy-PAs exhibited an enhanced current density of ~ 13.2 mA/cm2 at 1.23 V vs RHE, ABPE of ~ 1.5%, and a hydrogen evolution rate of 177 μmoles/min/cm2. Overall, rGO@CZTS/PPy-PAs showed 2.1-fold, 1.1-fold, and 1.4-fold enhancement in photocurrent activity over PPy-PAs, CZTS/PPy-PAs, and rGO/PPy-PAs, respectively. The usability of rGO@CZTS/PPy-PAs is established in the form of stable photocurrent for more than 200 min. These findings open new possibilities for developing modified PPy PAs as flexible PEs for efficient solar-driven PEC devices and give directions on improving flexible PEs for flexible and efficient solar-driven PEC systems.

The research on dye-sensitized solar cells (DSSCs) is in the advanced stage today. The only concern observed so far has been regarding its stability and efficiency. Its power conversion efficiency can be increased by incorporating various methods and materials based on nanotechnology. Several attempts have been employed to develop advanced methods for eco-friendly, commercially viable, and sustainable DSSCs to minimize the energy crisis in the future. Photoanode is one of the essential components of DSSCs that can be modified using different nanostructures to enhance its efficiency. The TiO2 nanoparticlebased photoanode with gold and silver has proven to be potent materials for getting efficient DSSCs. The plasmonic and quantum confinement effects also play a vital role in efficiency enhancement. In this review, we discuss numerous attempts made by researchers in the last decade to modify the photoanode and their progress. We also look at different types of nanostructures, such as quantum dots, metal oxide doping, layered structures, nanocomposites, and thin film formation, that improve the efficiency of DSSCs. Several methods were reviewed to modify photoanodes to optimize electron transportation, light scattering, trapping power, surface area, and reduce charge recombination. The trend in the efficiency enhancement of DSSCs using TiO2, Au, ZnO, Ag, and graphene nanostructures-based photoanodes have been explored in great detail.

Synthesizing nanostructured thin films of oxide semiconductors is a promising approach to fabricate highly efficient photoelectrodes for hydrogen production via photoelectrochemical (PEC) water splitting. In this work, we investigate the feasibility as an efficient photoanode for PEC water oxidation of zinc oxide (ZnO) nanostructured thin films synthesized via a simple method combined with sputtering Zn metallic films on a fluorine-doped tin oxide (FTO) coated glass substrate and subsequent thermal oxidation of the sputtered Zn metallic films in dry air. Characterization of the structural, optical, and PEC properties of the ZnO nanostructured thin film synthesized at varying Zn sputtering powers reveals that we can obtain an optimum ZnO nanostructured thin film as PEC photoanode at a sputtering power of 40 W. The photocurrent density and optimal photocurrent conversion efficiency for the optimum ZnO nanostructured thin film photoanode are found to be 0.1 mA/cm2 and 0.51 %, respectively, at a potential of 0.72 V vs. RHE. Our results illustrate that the ZnO nanostructured thin film has promising potential as an efficient photoanode for PEC water splitting.

Synthesizing one-dimensional nanostructures of oxide semiconductors is a promising approach to fabricate highefficiency photoelectrodes for hydrogen production from photoelectrochemical (PEC) water splitting. In this work, vertically aligned zinc oxide (ZnO) nanorod arrays are successfully synthesized on fluorine-doped-tin-oxide (FTO) coated glass substrate via seed-mediated hydrothermal synthesis method with the use of a ZnO nanoparticle seed layer, which is formed by thermally oxidizing a sputtered Zn metal thin film. The structural, optical and PEC properties of the ZnO nanorod arrays synthesized at varying levels of Zn sputtering power are examined to reveal that the optimum ZnO nanorod array can be obtained at a sputtering power of 20W. The photocurrent density and the optimal photocurrent conversion efficiency obtained for the optimum ZnO nanorod array photoanode are 0.13 mA/cm2 and 0.49 %, respectively, at a potential of 0.85 V vs. RHE. These results provide a promising avenue to fabricating earth-abundant ZnO-based photoanodes for PEC water oxidation using facile hydrothermal synthesis.

We report on the fabrication and characterization of an oxide photoanode with a zinc oxide (ZnO) nanorod array embedded in cuprous oxide (Cu2O) thin film, namely a ZnO/Cu2O oxide p-n heterostructure photoanode, for enhanced efficiency of visible light driven photoelectrochemical (PEC) water splitting. A vertically oriented n-type ZnO nanorod array is first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method and then a p-type Cu2O thin film is directly electrodeposited onto the vertically oriented ZnO nanorod array to form an oxide p-n heterostructure. The introduction of Cu2O layer produces a noticeable enhancement in the visible light absorption. From the observed PEC current density versus voltage (J-V) behavior under visible light illumination, the photoconversion efficiency of this ZnO/Cu2O p-n heterostructure photoanode is found to reach 0.39 %, which is seven times that of a pristine ZnO nanorod photoanode. In particular, a significant PEC performance is observed even at an applied bias of 0 V vs Hg/Hg2Cl2, which makes the device self-powered. The observed improvement in the PEC performance is attributed to some synergistic effect of the pn bilayer heterostructure on the formation of a built-in potential including the light absorption and separation processes of photoinduced charge carriers, which provides a new avenue for preparing efficient photoanodes for PEC water splitting.

입자 크기가 약 16 및 5 nm인 두 다른 크기의 TiO2 나노입자들과 titanium tetraisopropoxide (TTIP) binder 와 ethanol 용매만으로 제조된 코팅액을 사용하여 130 oC 저온 열처리로 ITO/PEN substrate 위에 메조다공성 TiO2 박막들을 형성하였다. 이들 TiO2/ITO/PEN 박막들을 활용한 유연 염료감응 태양전지들을 제작하여 광변환 특성을 비교 연구하였다. 크기가 다른 두 TiO2 나노입자들을 각각 단독으로 사용하여 제작된 cell들의 경우에 크기가 16 nm 인 TiO2 나노입자 cell이 5 nm인 나노입자 cell에 비해 박막의 porosity가 훨씬 크고 같은 질량에서 표면적이 훨씬 넓어 광변환 효율이 훨씬 높으나 염료 흡착량에 대해 상대적으로 작은 광전류는 입자간의 연결성에 기인되며 큰 입 자에 작은 입자를 10% 정도 혼합한 경우에 표면적 증가와 함께 입자간의 연결성을 강화시켜 큰 입자 단독으로 제작 된 cell에 비해 광변환 효율이 크게 증가됨을 확인하였다.