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Dye-sensitized solar cell (DSSC), the third generation photovoltaic technology is most promising alternative photovoltaic technology due to low-cost, stable electrical generation, good temperature stability, non-toxic emission during manufacturing, rapid efficiency enhancement and wider flexibility in design. The present study reviews the advanced techniques and research trends of ZnO compotization with TiO 2 in different nano-structures. Performance efficiency gap between the conventional silicon solar cell and DSSC is an intensely promoted area of research. It results in an efficient photoanode which further leads to the improvement in DSSC. Their performance is further enhanced using engineered nanostructured metal oxide photoanode. The study emphasizes on nano-compotization of conventional titanium dioxide with other metal oxide in different structures. It is one of the active research technologies for efficient DSSC. Comparative performance study shows that three dimensional and hybrid nanostructured TiO 2 /ZnO nanocomposite such as nanodonuts, nanoflower and 3D hierarchical heterostructure have better performance. Their open circuit voltage, short circuit current, fill factor and efficiency lies in the range of 0.76–0.82 V, 3.24–16.70 mA/cm 2 , 0.17–0.69% and 0.51–9% respectively. Thus they result in rapid electron transfer rate, slower charge recombination rate and higher surface area.

TiO2, TiO2–ZnO (TZ) nanocomposite and PANI (Poly aniline) have been synthesized by simple sol–gel and direct chemical method, respectively, for the application in Dye Sensitized Solar Cell (DSSC). Structural, morphological and optical analyses were carried out using XRD, SEM, EDAX, PL and FTIR. PANI film has been fabricated for solid state DSSC. The photovoltaic performance has been checked for both liquid state and solid state in outdoor and indoor environmental condition. The results show that for TZ showed better performance compared to the monophasic TiO2. Stability test showed that the solid state DSSC shows a better stability under constant illumination. Liquid state DSSC loses its efficiency by about 52.5 % while solid state to DSSC by about 13.3 % after 5 h of constant illumination.

Increasing energy demand and growing environmental concerns have driven the civilization towards cleaner energy-producing devices. Among the various clean energy devices, fuel cells have gained considerable attention due to their attractive features such as high efficiency, low or zero tail-end carbon emission, quiet operation, modular size, etc. The recent technological advances in the different components of the fuel cell are translated into new fuel cell devices and systems. The commercial application of fuel cells has been made feasible due to these technological advances. Research and development in the low-temperature fuel cells, particularly the polymer electrolyte fuel cell (PEFC), have been advanced more in comparison to the medium- and high-temperature fuel cells. The PEFC has been extensively tested in automobiles. The advent of the microbial fuel cell (MFC) and direct glucose fuel cell (DGFC) has added a new dimension to the low-temperature fuel cell technology. The more attractive application of MFC is often seen in the waste treatment and energy generation. Similarly, the fuel cells are also tested for unmanned machines, vehicles and space application. The medium- and high-temperature fuel cells are usually used as a stand-alone system. This chapter provides an overview of the technological advances and applications of the fuel cells.

The fuel cell and electrolyzer together may be an important alternative source for clean energy production. The oxygen-hydrogen produced in the water splitting reaction in an electrolyzer may also be used in any conventional combustion engines with a little or no modification of the existing engines. The sluggish oxygen reduction reaction (ORR) in these devices necessitates higher loading of catalysts in the cathode. However, the best catalyst used in fuel cell and electrolyzer is platinum and/or its derivatives. The use of metal free graphene based heteroatom doped ORR catalyst may be a promising alternative for conventional platinum electrocatalyst. In particular, nitrogen-doped Graphene synthesized from natural carbon based biomass material has the potential to be a sustainable, green and economical ORR. In this study, Assam silk cocoons was used to synthesize nitrogen doped graphene based catalyst via one step in-situ pyrolysis. The morphological and chemical characterization of the synthesized catalyst was carried out with the help of XRD, Raman, FTIR, TEM, EDS and XPS. The X-Ray diffractograms of the catalyst revealed presence of defect induced broad peaks at graphitic 002 and 004 peaks at 24.5° and 43°, respectively. The Raman spectra showed the presence of D-band, G-band and D′ band with an ID/IG ratio of 0.86. The EDS analysis confirmed the presence of 21.55 At% in-situ nitrogen in the synthesized catalyst. The morphological analysis through TEM showed the presence of multilayer graphene. The formation of in-situ nitrogen doped graphene catalyst was confirmed through X-ray photoelectron spectroscopy, which showed the presence of pyridinic and graphitic nitrogen. The synthesized electrocatalyst was later analyzed with the help of a rotating disk electrode for its catalytic activity in ORR.