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Abstract In this work, we have focused on the preparation of copper hexacyanoferrate/boron doped rGO composites (abbreviated as CuHCF/B-rGO) by employing simple co-precipitation technique subsequently processed with ultrasonication method. The XRD spectra confirmed the existence of the cubic structure of copper hexacyanoferrate with high crystalline peaks. The prepared nanocomposite morphology was evaluated by scanning electron microscopy (SEM), and confirmed CuHCF nanoparticles formation with flake-like and wrinkled sheets. Pure CuHCF nanostructures revealed good OER action at 430 mV to obtain 10 mA/cm2. The obtained CuHCF product OER activity can be further upgraded by incorporating the electrically conductive boron doped reduced graphene oxide matrix into CuHCF nanostructures, for the reason that the overpotential of the CuHCF/B-rGO was reduced to 380 mV to attain 10 mA/cm2 with 88 mV/dec Tafel slope value. The doping of heteroatom considerably improves charge-transfer resistance of metal hexacyanoferrate, giving a small resistance value of 2.97 Ω, which was lower than that of CuHCF (5.57 Ω) and CuHCF/rGO (4.31 Ω). Furthermore, the catalytic activity of the CuHCF/B-rGO was stable at prolonged hours with a small decay of 12.5%. Therefore, this work offers new approach to stimulate the catalytic performance of metal hexcyanoferrate by highly conductive carbon-based materials for water splitting performance.

Abstract Hydrogen production by photoelectrochemical (PEC) water splitting is a sustainable means that can avert the effects of global warming caused by fossil fuels. For decades, a suitable semiconductor that can absorb solar radiation in the visible region has been a focal research question. Hematite has a theoretical Solar-To-Hydrogen efficiency of 15% which is higher than the 10% benchmark for PEC water splitting. Despite being cheap, chemically stable, and bearing a desired band gap, hematite has not reached this projection due to challenges like band edge mismatch, short hole diffusion length and charge recombination. Various articles have shown hetero-structuring is a reliable solution to some challenges due to enhanced spectral range, enhanced carrier mobility, strong built-in electric field and thus increase in efficiency. However, these articles lack scientific rationale on the performance of hematite and its hetero-structures on different substrates, which is the basis for this review. Our analysis suggests that hetero-structure improves hematite’s PEC performance due to increased spectral range, enhanced carrier mobility and built-in electric field. This review article is organized as follows: a brief PEC background, performance parameters, Physical and Crystallographic properties of hematite, device configurations, performance of hematite and its hetero-structures on different substrates. Graphical Abstract

Significant financial and environmental challenges are associated with using platinum electrodes as counter electrodes (CEs) in dye-sensitized solar cells (DSCs). This work uses rice husk, an agricultural waste, to create active carbon that is appropriate for DSC CEs in response to these difficulties. A simple spray pyrolysis technique created activated carbon obtained from rice husks. The DSC employing activated rice husk carbon as the CE demonstrated a conversion efficiency of 6.06%, slightly lower than the 8.21% efficiency achieved with a platinum electrode-based cell. However, this performance gap is overshadowed by the substantial cost reduction enabled by the utilization of low-cost activated carbon compared to noble metal alternatives. This result introduces promising avenues for investigating the use of agriculturally derived carbon materials as workable and affordable options for platinum CEs in DSCs, thereby contributing to the sustainable advancement of photovoltaic systems. Even though the performance of DSC that uses activated carbon derived from rice husk in CE is slightly lower than its counterparts based on platinum, the cost reduction due to the use of low-cost activated carbon with noble metal is significant.

Abstract In this study, a natural dye from the flowers of Mussaenda erythrophylla extracted separately in ethanol and de-ionized water was employed as a photosensitizer in DSSCs. The quantitative phytochemical analyses were performed on both extracts. The existence of flavonoids (anthocyanin) and chlorophyll a pigments in the ethanol extract of the dye was confirmed by the UV–Visible spectroscopy. The stability study performed on the said ethanol extract confirmed that the dye extracted in ethanol was stable in the dark and did not degrade for nearly 50 days. The presence of the dye molecules and uniform adsorption of them on the P25-TiO2 surface were confirmed by fourier transform infrared spectroscopy and atomic force microscopy, respectively. Moreover, the influence of dye concentration and pH on the optical properties of the dye was also studied. The natural dye extracted in ethanol was employed in DSSCs, fabricated by utilizing the said dye sensitized P25-TiO2 photoanodes, $${I}^{-}$$ I - / $${I}_{3}^{-}$$ I 3 - electrolyte, and Pt counter electrode. Photovoltaic performances of the fabricated devices were determined under simulated irradiation with the intensity of 100 mWcm–2 using AM 1.5 filter. The device fabricated with the P25-TiO2 photoanode sensitized by the dye extracted in ethanol at pH = 5 exhibited the best power conversion efficiency (PCE) of 0.41% with the JSC of 0.98 mAcm–2 which could be attributed to the optimum light absorption in the visible region of solar spectrum by the chlorophyll a and anthocyanin molecules in the extracted natural dye.

Engineering and designing unique morphologies is a smart way to tune the characteristics of the material. Here, in this work, beyond the existing knowledge, we have focused on developing novel methods for synthesis of high performance CuCo2S4 (CCS) and Graphene nanostructured material for supercapacitor applications. We first developed a rich mesoporous CCS-graphene structure, and for further enhancement of electrochemical performance, we incorporated nitrogen(N) and sulfur(S) into the graphene (NS–pG) framework. Further, through a controllable synthesis procedure dominated by nucleation and growth mechanism, we could obtain a highly ordered array of CuCo2S4 microspheres on the surface of graphene sheets confirmed by FESEM images. Successful material modifications have led to realize a novel CuCo2S4/NS–pG composite structure with remarkable electrochemical performance. The as-obtained, tuned hybrid CuCo2S4/NS–pG composite structure exhibited great surface area, excellent structural stability, and high electrical conductivity due to its modified morphology. Based on these unique advantages, the hybrid CuCo2S4/NS–pG composite-based electrode revealed exceptional specific capacitance of 1357.8 F g−1 at 1 A g−1, superior cycle performance of 95.9% after 5000 cycles, and distinguished maximum energy and power density of 80.59 W h kg −1 and 10479.53 W kg −1, respectively, which are superior to the performance of any reported CuCo2S4 electrodes.

Here we present the optoelectronic properties of pure inorganic lead-free halide perovskites in the form of Cs _2 AgBi X _6 ( X = Br, Cl, F, I) using the density functional theory calculations on cubic phase (Fm $\mathop{3}\limits^{̅}$ m) and tetragonal phase (I4/m). First, all the structures of the two phases were optimized at the PBE level. Structural, electronic, optical properties, phonon, and thermal properties of Cs _2 AgBi X _6 in cubic (Fm $\mathop{3}\limits^{̅}$ m) and tetragonal phases (I4/m) were obtained using the VASP code. Tetragonal phases of all compounds of the form Cs _2 AgBi X _6 , except Cs _2 AgBiBr _6, are reported here for the very first time. Among all the Cs _2 AgBi X _6 ( X = F, Cl, Br, I) structures, the cubic phase of Cs _2 AgBiBr _6 was seen to have the highest absorption coefficient along with prominent electronic features that are favorable for optoelectronic applications. Thus, the cubic phase of Cs _2 AgBiBr _6 was selected as the host lattice and bromine atoms were partly replaced with chlorine and iodine atoms. Electronic and optical properties of these mixed halide compounds of Cs _2 AgBiBr _6−x F _x , Cs _2 AgBiBr _6−x Cl _x, and Cs _2 AgBiBr _6−x I _x where x = 1, 2, 3, 4, 5 are investigated with hybrid functional HSE06 level. The electronic structure revealed that these mixed compounds exhibited indirect band gap nature regardless of the halide substitution (different x concentration) and the band gap of Cs _2 AgBiBr _6 could be varied with the substitutions of fluorine, chlorine, and iodine atoms. Our in-depth analysis shows that Cs _2 AgBiBr _6 and their mixed halides have the potential to become active double perovskite materials for photovoltaic applications and as photocatalysts for water splitting.