Flexible polypyrrole activated micro-porous paper-based photoanode for photoelectrochemical water splitting
Graphical abstract
Introduction
Photosynthesis is one of the key tools to utilize solar energy by converting or storing it in the form of chemical energy for a library of day-to-day uses [1]. The future potential and commercial viability of photosynthesis have stimulated worldwide researchers to design an efficient and stable artificial light-harvesting system to mimic the process using various heterostructured materials [2,3]. Further, the increasing deficit in the demand/supply of fossil fuels followed by global warming due to carbon emission, demands to development of alternative and affordable renewable fuel. According to the recently published report from the US energy department and recent energy-related research, hydrogen generation via water splitting has considered one of the futuristic potential approaches to develop alternative clean fuel technology [[4], [5], [6], [7], [8], [9]]. Moreover, the developed photoelectrodes for hydrogen generation are lacking either with the conversion efficiency or with stability, including their cost-effectiveness. Further, to make the use in harsh physiological conditions, the development of a flexible electrode became an attractive solution, as demonstrated for numerous other applications [10]. The trending practice of flexible energy devices, comprising of the flexible and conductive substrate is a strategic-aiding aspect for the speedy-propagation of flexible electronics. Owing to their low-cost, flexibility in nature, and vastly porous structural framework, the papers, and textiles have been employed in the recent past as an ideal substrate [11]. However, due to their insulating nature, the surface modification with the electrically conductive materials is required for efficient carrier transport [ESI Table 1] [[12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23]]. The combination of paper with the conductive channels is recently reported for various successful applications. Likewise, nano-fibrillated cellulose (NFC), where its nano-channels are filled with aqueous electrolytes is explored for efficient paper-based super-capacitor [24]. Further, paper-based ion-selective electrodes are emulated as a single-strip ready-to-use sensor for Na(I), K(I), and Iodide ions based on Nernstian response down to submicromolar limits of detection [25].
The successful use of paper-based electronics is also reported for the various applications in biomedical, consumer electronics, and military sectors [[26], [27], [28], [29], [30]], however, not much has been explored towards designing artificial hydrogen energy harvesting systems.
Recently, polymers have been attracting increasing attention for designing photocatalysts owing to their unique delocalized conjugated system, high charge carrier mobility, narrow and tunable optical band gaps, and efficient UV–Vis light absorption [31]. Among them, polypyrrole (PPy) has gained particular interest as a photocatalyst for PEC water splitting, since it has optical band-gap, visible light absorption property, environmental stability, better redox property, and commercial availability of initial monomers [ESI Table 2] [[32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42]]. Herein, in this work for the first time, we have utilized the conductive nature, large solar absorption, and suitable band straddling (with water redox) of Polypyrrole (PPy) to use it for developing laboratory filter paper-based flexible, effective, and stable photoanodes (PAs) for photoelectrochemical (PEC) water splitting [36,[43], [44], [45]]. In particular, the fabrication strategy emulates an in-situ polymerization scheme to render conductivity of the laboratory filter paper by depositing polypyrrole polymer, while still retaining the vulnerable macroporous framework of filter paper.
Section snippets
Fabrication procedures of PFP-PAs
Scheme 1 presents an illustrative schematic of the design and fabrication procedures of PFP-PAs on commonly available laboratory filter paper. In a typical experiment, conductive and flexible PFP-PAs were first prepared by in-situ polymerization scheme utilizing laboratory filter paper by depositing polypyrrole polymer. The conductive polymer-filter papers were prepared by the one-step in-situ polymerization method.
Briefly, the filter paper was dipped in the varied concentration of oxidizing
Structural and optical characterization of PFP-PAs
PFP-PAs were optimized in terms of conductivity (preliminary measured with a digital multimeter, ESI Fig. 2) of fabricated electrodes w.r.t. varying concentration of oxidizing agent i.e. FeCl3. The PFP-PAs fabricated with 0.13 M ferric chloride hexahydrate showed better characteristics with the thickness of ~250 μm, thereby it was chosen for further studies in terms of detailed characterization and subsequently PEC water splitting discussed further. Fig. 1 (a & b) portrays the SEM images of the
Conclusions
In summary, we establish a proof-of-concept on the value-added transformation of laboratory-based filter paper into an efficient, flexible, and stable photoanode (PAs) for PEC water splitting by coating them with photoactive polypyrrole through in-situ polymerization. The effect of oxidant concentration on the photoactivity of the PAs is studied. The optimally fabricated PAs show excellent PEC characteristics with a measured maximum current density of ~9.5 mA/cm2 (1.23 V. RHE), ABPE, and IPCE
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
AT acknowledges DST-INSPIRE Fellowship for doctoral study. PD acknowledges SERB for the funding support under SERB Women Excellence Award (WEA/2020/000022) project and Department of Science and Technology (Grant No.: DST/TMD/HFC/2k18/138), for financial support.
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