Photo-supercapacitors (PSCs) combine functions of energy harvesting and storage in a single device, and in this study, a new architecture for a PSC is designed and implemented. Cadmium sulfide (CdS) quantum dots/hibiscus (hb) dye co-sensitized TiO2 is used as the solar cell. Poly­(3,4-ethylenedioxypyrrole) (PEDOP)@manganese dioxide (MnO2) is employed as the counter electrode (CE) for the solar cell and also as the electrodes for the symmetric supercapacitor. The two ends of a long flat current collector support two spatially separated PEDOP@MnO2 coatings, which serve as the CEs for the TiO2/hb/CdS photoanode and yet another PEDOP@MnO2 electrode in sandwich configurations. In this cell, under 1 sun (100 mW cm–2) illumination, the TiO2/hb/CdS photoanode undergoes charge separation and by channeling the photocurrent to the PEDOP@MnO2 electrodes, the symmetric cell part is charged to a voltage of 0.72 V. The PSC delivers a specific capacitance of 183 F g–1, an energy density of 13.2 Wh kg–1, and a power density of 360 W kg–1 at a discharge current density of 1 A g–1. During the self-discharge process, PEDOP@MnO2-based PSC retains a voltage of 0.72 V up to 500 s and maintains a stable voltage of 0.5 V thereafter. The TiO2/hb/CdS photoanode with the PEDOP@MnO2 CE in an aqueous polysulfide–silica gel electrolyte delivers a power conversion efficiency of 6.11%. This demonstration of a novel PSC opens up opportunities to develop new architectures for efficiently combining energy conversion and storage.

Long-lasting Li−Se cells with a Se/graphite platelet nanofiber (GPNF) composite is prepared for the first time, and it shows a reversible capacity of 489 and 384.7 mAh g Se −1 after 200 and 350 charge/discharge cycles, respectively. It shows superior rate capability and low Se polarization even with a high Se (75 wt %) proportion. It also shows higher capacity and better cycling stability compared to conventional Se/carbon material composites (with graphene oxide (GO), reduced GO, and carbon nanotubes). The effectiveness of GPNFs as a conductive support and for inhibiting the shuttle and dissolution of polyselenides in the electrolyte is also confirmed by conducting atomic force microscopy studies. Nanoscale current maps of Se/GPNFs reveal the presence of homogeneously distributed high-current domains, which are retained even after the first discharge. In contrast, the pristine Se electrode is characterized by predominant low-current regions after the first discharge. The ability of GPNFs to enable the preparation of durable and easily processable Li−Se cells is demonstrated.

The hierarchical heterostructure of NiMoO4@NiMnCo2O4 (NMO@NMCO) with furry structures of NMCO juxtaposed with NMO nanowires are endowed with multiple electrochemically active and accessible sites for ion storage, thus delivering an ultrahigh specific capacitance of 2706 F g–1, nearly two-fold times greater than that of sole NMCO. Electrodeposition of an overlayer of a highly robust and electrically conducting polymer, poly­(3,4-propylenedioxythiophene) (PProDOT), not only improves the energy storage performance but also assists the binary oxide cathode in retaining its structural integrity during redox cycling. Coupling with an anode of porous flaky carbon (FC) derived from groundnut shells results in an asymmetric supercapacitor of FC//PProDOT@NiMoO4@NiMnCo2O4, which delivers an outstanding capacitance of 552 F g–1, energy and power density ranges of 172–40 Wh kg–1 and 0.75–10 kW kg–1, respectively, and a remarkable cycle life of 50 000 cycles, with ∼97.8% capacitance retention, over an operational voltage window of 1.5 V. From an application perspective, the charged supercapacitor was connected to a complementary coloring reversible electrochromic device (ECD) of Prussian blue//PProDOT, and the ECD state transformed from a pale-blue to a deep blue hue, thus signaling the efficient utilization of energy stored in the supercapacitor. The energy-saving attribute of the ECD was realized in terms of an integrated visible-light modulation of 39% that accompanied the optical transition. Deployment of low-cost devices at homes and commercial spaces, capable of storing and saving energy, is the way forward, and this is one significant step in this direction.

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Semiconducting cobalt tungstate flanked by carbon (CoWO4@C) polyhedral microstructures with smooth facets and zinc ferrite (ZnFe2O4) polydisperse interconnected nanoparticles via intrinsic mechanisms of hole polaron transfer from Co3+ to Co2+ sites and electron hopping between Fe2+ and Fe3+ states, respectively, were endowed with high room-temperature electrical conductivities (>0.9 mS cm–1), thus enabling the fabrication of a high-performance asymmetric supercapacitor (ASC) possessing an outstanding rate capability as well as a good trade-off between power (P) and energy (E) densities. Furthermore, electrochemical response comparison of CoWO4@C//ZnFe2O4 ASCs encompassing three different electrolytes (aqueous KOH, KOH–PEO gel, and KOH–PVA gel) revealed that the KOH–PEO gel cell outperformed the other two ASCs, with a specific capacity (SC) of 339 F g–1 (at 1 A g–1) and E max and P max of 105 Wh kg–1 and 3.2 kW kg–1 achieved over an operational voltage window of 1.5 V while retaining 97% of the original SC after 10,000 cycles. With KOH and KOH–PVA gel, while the P max remained the same, SCs of 300 and 322 F g–1 and E max’s of 93 and 100 Wh kg–1 were obtained. The high ionic conductivity (81.6 mS cm–1) of the KOH-PEO gel is attributed to the hydrogen bonded networked structure of the gel with free spaces that allows ions to move freely within the polymer matrix. Further, the oxygens along the polymer chains ensure a high dissociation of KOH. The gel also serves as an ion-reservoir and these factors cumulatively resulted in the enhanced performance of the ASC. This study showcases that scalable, low-cost, leak-proof supercapacitors can be fabricated using environmentally friendly electroactive materials that can be synthesized easily using simple wet chemistry techniques.