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Copper(II)phthalocyanine-incorporated metal organic framework (CuPc/MOF) composite material was synthesized for application as an electrocatalyst for hydrogen evolution reaction (HER). The composite exhibited excellent electroactivity compared to the unmodified MOF, as confirmed by the diffusion coefficients (D) values of 3.89 × 10−7 and 1.57 × 10−6 cm2 s−1 for MOF and CuPc/MOF, respectively. The D values were determined from cyclic voltammetry (CV) experiments performed in 0.1 mol L−1 tetrabutylammonium perchlorate/dimethyl sulfoxide (TBAP/DMSO) electrolyte. The Tafel slope determined from the CV data of CuPc/MOF-catalysed HER for 0.450 mol L−1 H2SO4, was 176.2 mV dec−1, which was higher than that of the unmodified MOF (158.3 mV dec−1). The charge transfer coefficients of MOF and CuPc/MOF were close to 0.5, signifying the occurrence of a Volmer reaction involving either the Heyrovsky or the Tafel mechanism for hydrogen generation. For both MOF and CuPc/MOF, the exchange current density (i0) improved with increase in the concentration of the hydrogen source (i.e. 0.033–0.45 mol L−1 H2SO4) Nonetheless, the CuPc/MOF composite had a higher i0 value compared with the unmodified MOF. Thus CuPc/MOF has promise as an efficient electrocatalyst for HER.

The quest for smart sensors with excellent sensitivity, fast response and high reproducibility for hydrogen gas detection has been ongoing for decades. In this work, polyaniline (PANI) was doped with a cobalt-based zeolitic benzimidazolate framework material (CoZIF), to form PANI-CoZIF metal-organic framework (MOF) composite material, which was applied in the electrochemical hydrogen gas sensing. The synthesis of PANI-CoZIF composite was performed by the chemical oxidative polymerization of aniline in the presence of 3.6 wt% CoZIF. The structural properties of the synthesized materials (i.e., PANI, CoZIF, and PANI-CoZIF) were studied by ultraviolet-visible (UV-vis), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman spectroscopic analyses, as well as by thermogravimetric analysis (TGA). Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and high-resolution transmission electron microscopy/selected area electron diffraction (HR-TEM/SAED) techniques were used for morphological characterization. Both SEM and TEM analyses revealed the grafting of CoZIF on to the surface of PANI in the PANI-CoZIF composite material. XRD patterns and SAED results indicated that PANI and the composite were amorphous in nature. Spectroscopic analyses by FTIR and Raman techniques revealed the coexistence of CoZIF and PANI in the MOF composite material (PANI-CoZIF), which was also confirmed by the high intensities of the characteristic X-ray peaks of ZIF and the polymer. From Tauc plot analysis, it was found that PANI and PANI-CoZIF had band gap energy (Eg) values of 2.5 and 2.3 eV, respectively, indicating that they are both semi-conductors. TGA data confirmed an enhanced thermal stability of PANI-CoZIF compared with pristine PANI. Cyclic voltammetry (CV), chronoamperometry (CA), and Tafel and turn over frequency (TOF) analyses were used to study the electrocatalytic behavior of PANI and PANI-CoZIF in the hydrogen evolution reaction (HER) for gas sensing. There were very significant increases in the TOF value and the magnitude of the catalytic current for PANI-CoZIF compared with pristine PANI as electrocatalysts in the HER. Thus, PANI-CoZIF composite has a greater potential as a suitable electrocatalyst for practical application in the hydrogen fuel technology and hydrogen gas sensing.

Herein, we report on the in-situ chemical polymerization of polyaniline (PANI) doped with zinc-based zeolitic benzimidazolate framework (ZnZIF) to fabricate the PANI-ZnZIF composite for electrochemical hydrogen gas sensing. Fourier-transform infrared and Raman studies of PANI-ZnZIF composite revealed the presence of functional groups corresponding to both ZnZIF and PANI. Both X-ray diffraction and simultaneous thermal analyses showed the co-existence of both PANI and ZnZIF in the composite supported by the decrease in crystallite size and the improvement in the thermal stability, respectively. The scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and selected area electron diffraction revealed that PANI nanofibers wrapped the cube nanofiber-like structures of ZnZIF. The square wave voltammetry, cyclic voltammetry (CV) and chronoamperometry presented good electrochemical performance indicated by an increase in current response with 3 wt% loading of ZnZIF. The high electrochemical current response is due to extraordinary specific surface area, more accessible active sites available for the electrolyte provided by ZnZIF and high conductivity supplied by PANI. Moreover, Tafel parameters and Turnover frequency values derived from CV showed an improvement in the catalytic hydrogen evolution of PANI-ZnZIF composite. The resulting PANI-ZnZIF composite was found to be highly responsive to hydrogen gas as indicated by higher current response and sensitivity (10.8 μA mM H2), faster steady state response time of 4 s accompanied by lower detection limit of 5.27 μM as compared to pure PANI.

A dye-sensitized solar cell (DSSC) is an unconventional opportunity for silicon solar cells, owing to their flexibility, transparency, and low cost. The necessity for DSSCs to capture more of the sunlight radiation was the motivating force for the fabrication of semiconductor materials based on high surface area. The constituents of DSSC syndicate form a solar cell device. The main components in DSSCs are the conducting substrate, dye, photoanode, catalyst, and electrolyte. The photoanode is a well-known element that generates the energy conversion efficiency. There are different photoanode materials that have been studied to date. Amongst photoanode materials, titanium oxide (TiO2) materials are extensively documented, explored, and considered. In this chapter, effort will be made to survey the strategies to advance the energy efficiency of TiO2-based photoanodes with the introduction of metal-organic frameworks (MOFs) in DSSCs to suppress the recombination rate and electron loss. It was seen that to attain a high conversion yield in DSSCs, it is for very fast collection of produced ion carriers before electron re-combination. This chapter is devoted to the TiO2 and MOF photoanode, their properties, and various improvement approaches.

Exploiting low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER) is an important route to solve the energy crisis and environmental pollution. HER process plays a vital role in many energy storage and conversion systems including water splitting, rechargeable metal–air batteries and the unitised regenerative fuel cells. The platinum-based catalysts are regarded as best electrocatalysts for the HER; nevertheless, they are very exorbitant and scarce. Therefore, it is necessary to develop efficient electrocatalysts based on carbon materials. Graphene oxide (GO), for instance, is a monolayer structure with a high contribution of sp2 hybridised carbon atoms, and various oxygen-containing surface functional groups have attracted the attention of a worldwide research community in the last decades due to its various potential applications linked to the unique combination of properties, such as hardness, physical and chemical stability, high specific surface area, electron mobility and heat transfer. It can be easily manufactured by simple and scalable chemical oxidation approaches from graphite, the reduction of GO into reduced GO (rGO) is a widely used method to obtain graphene. In HER, GO can also be incorporated with metals and porous materials for synergetic effect as co-catalysts for enhancement of electrocatalytic activities. On the other hand, metal–organic frameworks (MOFs) are crystalline materials with porous network structure. They possess various compositions, large surface area, tunable pore structures and are easily functionalised. Recently, MOF‐based electrocatalysts have been rapidly developed with excellent catalytic performance, demonstrating a promising application prospect in HER. In this chapter, the background on hydrogen energy and HER structure, category and synthesis of GO and MOFs are discussed. The application of GO- and MOF-based electrocatalysts for HER is discussed in detail. Their HER parameters such as Tafel slope (b) and exchange current density (i0) are emphatically discussed and followed by the synergetic effect of HER studies of GO/MOF composites as an alternative electrocatalyst for future hydrogen production and storage via HER mechanism.

Pd-supported copper phthalocyanine/metal organic frameworks (Pd@CuPc/MOF) composite was synthesized by the reaction between CuPc and MOF followed by electroless Pd plating. The structural properties of MOF, Pd@MOF and Pd@CuPc/MOF composite were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), simultaneous thermal analysis (STA), ultraviolet–visible spectroscopy (UV–vis), scanning electron microscopy (SEM/EDS) and Brunauer-Emmett-Teller (BET). The XRD, UV–vis and FTIR analyses showed that Pd was coated on CuPc/MOF composite. SEM and EDS results revealed that Pd nanoparticles were well-dispersed and anchored tightly on the composite. The thermal stability of MOF increased upon addition of Pd and CuPc. The electrochemical hydrogen evolution reaction (HER) performance of the synthesized materials was studied by cyclic voltammetry (CV) and Tafel analysis. The Tafel slope of the composite was 176.9 mV/dec and the transfer coefficient of 0.67 which is close to 0.5. The HER results revealed that the Pd@CuPc/MOF composite has better catalytic characteristic such as high catalytic activity and lowest onset potential compared to MOF. More importantly, the significant enhancement of HER performance at ambient temperature for the composite with Pd content can be ascribed to the hydrogen spillover mechanism in such system.

Polyaniline-metal organic framework (PANI/MOF) composite was prepared by chemical oxidation of aniline monomer in the presence of 3.6 wt% MOF content for hydrogen evolution reaction (HER). The structure, morphology and properties of the fabricated composite were investigated. There was a clear interaction of MOF on the backbone of the PANI matrix through electrostatic interaction as investigated by both Raman and Fourier transform infrared analyses. The MOF exhibited irregular crystals with further wrapping of MOF by PANI matrix as evidenced by both scanning electron microscopy and transmission electron microscopy studies. The PANI composite showed some nanorods and microporous structure. The energy band gap values of PANI and its composite were found to be 1.50 and 1.35 eV, respectively. The thermal stability of the neat PANI increased upon composite formation, which was due to a stabilizing effect of MOF and a change in morphology of the composite. The catalytic effect of MOF, PANI and PANI/MOF composite on HER was studied using exchange current density (i0) and charge transfer coefficient determined by the Tafel slope method. A drastic increase in catalytic H2 evolution was observed in the composite. In addition, the Tafel slope values of PANI and the composite decreased with increasing the concentration of the acid, suggesting the Volmer reaction coupled with either Heyrovsky or Tafel reaction. The i0 increased with increasing the acid concentration and in an order of PANI/MOF > MOF > PANI at various concentrations.

Advanced materials for hydrogen evolution reaction are central to the area of renewable energy. Here, we developed a solvothermal synthesis of metal organic framework (MOF) nanoparticles decorated with poly (3-aminobenzoic acid) (PABA) referred as MOF-3.6 wt.%-PABA and MOF–5 wt.%-PABA composites. The parent material (MOF) and composites were characterized by ultraviolet visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDS, EDX), selected area electron diffraction (SAED) and cyclic voltammetry (CV). Detailed structural and morphological characterizations established that PABA interacts with MOF on the external surface as observed by appearance of rough surface of the composites. The XRD and SAED showed that MOF and composites are crystalline and the presence of PABA did not alter the crystallinity of the material. Experiments probing the thermal, electrochemical and photophysical properties revealed that the composites were very stable and robust and had exceptionally properties. Significant hydrogen evolution reaction (HER) using CV and Tafel plots, was generated by MOF and composites in dimethyl sulfoxide/tetrabutylammonium perchlorate (DMSO/TBAP) supporting electrolyte in the presence of hydrogen source by applying a negative potential to the electrode.

A novel graphenated-polyaniline (GR-PANI) nanocomposite sensor was constructed and used for the determination of anthracene. The direct electro-oxidation behavior of anthracene on the GR-PANI modified glassy carbon electrode (GCE) was used as the sensing principle. The results indicate that the response profile of the oxidation of anthracene on GR-PANI-modified GCE provides for the construction of sensor systems based on amperometric and voltammetric signal transductions. A dynamic linear range of 0.012–1000 μM anthracene and a detection limit of 0.0044 μM anthracene were established for the sensor system.

Electrochemiluminescent films have been formed by electrodepositing polyaniline, PANI, in the presence of [Ru(bpy)2PIC]2+; bpy is 2,2′-bipyridyl and PIC is (2,2′-bipyridyl)-2(4-carboxylphenyl) imidazo [4,5][1,10] phenanthroline. The homogeneous charge transport diffusion coefficient, DCT, for the Ru2+/3+ couple within the PANI film is 2.6 ± 0.9 × 10−10 cm2s−1. The large DCT facilitates a fast regeneration of Ru3+ and, coupled to a relatively rigid microenvironment, results in a high ECL intensity in the presence of tripropylamine as a co-reactant compared to [Ru(bpy)3]2+. Significantly, despite the conducting nature of the polymer backbone, the [Ru(bpy)2PIC]2+ loaded PANI has the highest efficiency, 1.00%, yet reported for a surface confined ruthenium complex. Keywords: Electrochemiluminescence, Polyaniline, Ruthenium

Charge transfer reactions of electroactive reagents in pure Nafion film are generally slow due to Nafion's compact nature and the poor diffusion of ionic species within the film. Cationic reagents, such as tris(bipyridine)ruthenium(II) ion ([Ru(bpy)3]2+), migrate into the electro-inactive hydrophobic region of the ionomer causing a loss in the electrochemical contact of the cationic material with the electrode. A highly dispersive gold nanoparticle (AuNp) dotted 4-nitrophenylazo (NPA) functionalised graphene (G) nanocomposite (AuNp/G/NPA) has been prepared and incorporated into Nafion on a glassy carbon (GC) electrode surface, in order to improve the electroactivity of the cationic reactant within the Nafion film. The Nafion nanocomposite-modified electrode efficiently loaded large amount of [Ru(bpy)3]2+ cationic redox probe. The sensitivity of the functionalised Nafion electrode was determined by the rate at which the Ru2+ sites were regenerated within the film. In comparison to pure Nafion film, the AuNp/G/NPA/Nafion nanocomposite film exhibited 100% relative electroactivity, 30% increase in peak currents and 34.9% reduction in charge transfer resistance.

A novel generation 2 poly(propylene imine)-co-polypyrrole conducting dendrimeric star copolymer (G2PPI-co-PPy) was synthesised electrochemically by oxidative copolymerization of pyrrole and pyrrole-functionalised dendrimer (G2PPI-2Py) in LiClO4 NMR spectra of G2PPI-2Py gave a new chemical shift at 8.1 ppm for N = CH, which confirmed the incorporation of 2-pyrrole aldehyde into the PPI dendrimer structure. Strong FT-IR bands appeared at 1630 cm−1 for N = C in the dendrimer moiety and at 729 cm−1 for C-H at the α-position of the PPy ring. Electroanalysis of the polymer films deposited on Pt electrode indicated that G2PPI-co-PPy has a lower electrochemical charge transfer resistance (Rct) value compared to PPy. The decrease in Rct is due to the increase in the conjugation length of the polymer as a result of the linking of the highly conjugated PPy to the PPI dendrimer. Bode impedimetric analysis indicates that Pt|G2PPI-co-PPy is a semiconductor with a maximum phase angle shift of 45.3° at 100 MHz. The scanning electron microscopy (SEM) image of G2PPI-co-PPy revealed conical PPy structures growing around a spherical core as predicted by the reaction mechanism for the formation of the dendritic star co-polymer.

A novel hybrid-hybrid nanocomposite based on 4-tetranitro copper(II)phthalocyanine (TNCuPc) grown on metal organic frameworks (MOF) as a noble metal-free catalyst for hydrogen evolution reaction (HER) was developed by a simple impregnation method. The structure, surface area and the morphology of the bare MOF, TNCuPc and the TNCuPc/MOF composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, Brunauer-Emmet-Teller, scanning electron microscopy, transmission electron microscopy and simultaneous thermal analysis. The electrocatalytic activity of the samples towards the HER was evaluated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry, exchange current density, i0, Tafel slope value, b, as well as charge transfer coefficient, α. The spectroscopic analyses indicated a successful synthesis of TNCuPc and its composite. The morphological results showed the development of rod-like structures of TNCuPc on the surface of the MOF. The composite exhibited an onset potential of about −0.713 V vs. Ag/AgCl in 0.1 M TBAP/DMSO and 0.3 M H2SO4 solutions, which is 44 mV and 9 mV more positive than that of MOF and TNCuPc respectively. The composite showed the rate determining step (RDS) to be the Volmer reaction in conjunction with either Heyrovsky or Tafel reaction as the RDS due to the Tafel slope value of 147 mV/dec and an α of 0.4. The i0 value of the TNCuPc/MOF composite was about 1.6 times that of the bare MOF. The EIS results showed the charge transfer resistance (Rct) of 12.6 kΩ for the TNCuPc/MOF composite as compared to MOF and TNCuPc values of 41 and 18.6 kΩ, respectively, demonstrating an excellent conductivity of the composite. In addition, Rct values of materials follow the sequence, blank

A thin film of the novel surface active ECL luminophore, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene, BODIPY, is used to demonstrate that the ECL turn on potential can be controlled through the identity of the co-reactant. The films were very stable when in contact with organic solvents and surface coverages of 1-2 nmol cm−2 are observed. Significantly, the potential at which ECL is generated is dictated by the identity of the co-reactant, either benzoyl peroxide or hydrogen peroxide, which opens new avenues for multi-analyte detection by changing the identity of the co-reactant rather than the dye. Keywords: Electrochemiluminescence (ECL), BODIPY, Self assembled monolayer, Optical sensor

Polyaniline-based metal-organic framework (PANI/MOF) composite was synthesized by chemical oxidation of aniline monomer in the presence of MOF content for practical usages as effective hydrogen production. PANI and composite were characterized by ultraviolet visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopy, atomic absorption spectroscopy (AAS), powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDS, EDX), selected area electron diffraction (SAED) and cyclic voltammetry (CV). Detailed structural and morphological characterizations established that PANI is wrapping MOF. The XRD, Raman and FTIR analyses showed that MOF was incorporated on the backbone of PANI through electrostatic interactions. This was supported by AAS analysis, revealing the amount of copper metal present in the composite. The determined energy band gap of the composite was in good agreement with previously reported catalysts for hydrogen evolution reaction (HER). Experiments probing the thermal, electrochemical, HER and photophysical properties revealed that the composite was very stable and robust and had exceptionally properties. Significant HER was generated by the composite in dimethyl sulphoxide/tetrabutylammonium perchlorate (DMSO/TBAP) supporting electrolyte in the presence of hydrogen source by applying a negative potential to the electrode. PANI and MOF also generated a weak HER as compared to composite.