Muhammad Arif Nadeem

Highly Porous Carbon Derived from MOF-5 as a Support of ORR Electrocatalysts for Fuel Cells

The development of highly competent electrocatalysts for the sluggish oxygen reduction reaction (ORR) at cathodes of proton-exchange membrane fuel cells (PEMFCs) is extremely important for their long-term operation and wide applications. Herein, we present highly efficient ORR electrocatalysts based on Pt/Ni bimetallic nanoparticles dispersed on highly porous carbon obtained via pyrolysis of a metal-organic framework MOF-5. In comparison to the commercial Pt/C (20%), the electrocatalyst Pt-Ni/PC 950 (15:15%) in this study exhibits a pronounced positive shift of 90 mV in Eonset. In addition, it also demonstrates excellent long-term stability and durability during the 500-cycle continue-oxygen-supply (COS) accelerating durability tests (ADTs). The significantly improved activity and stability of Pt-Ni/PC 950 (15:15%) can be attributed to the Pt electron interaction with Ni and carbon support as has been proved in X-ray and microscopic analysis.

Fabrication of CuFe2O4/α-Fe2O3 Composite Thin Films on FTO Coated Glass and 3-D Nanospike Structures for Efficient Photoelectrochemical Water Splitting

Recently, photoelectrochemical conversion (PEC) of water into fuel is attracting great attention of researchers due to its outstanding benefits. Herein, a systematic study on PEC of water using CuFe2O4/ α-Fe2O3 composite thin films is presented. CuFe2O4/ α-Fe2O3 composite thin films were deposited on two different substrates; (1) planner FTO glass and (2) 3-dimensional nanospike (NSP). The films on both substrates were characterized and tested as anode material for photoelectrochemical water splitting reaction. During PEC studies, it was observed that the ratio between two components of composite is crucial and highest PEC activity results were achieved by 1:1 component ratio (CF-1) of CuFe2O4 and α-Fe2O3. The CF-1 ratio sample deposited on planar FTO substrate provided a photocurrent density of 1.22 mA/cm2 at 1.23 VRHE which is 1.9 times higher than bare α-Fe2O3 sample. A significant PEC activity outperformance was observed when CF-1 ratio composite thin films were deposited on 3D NSP. The highest photocurrent density of 2.26 mA/cm2 at 1.23 VRHE was achieved for 3D NSP sample which is around 3.6 times higher than photocurrent density generated by α-Fe2O3 thin film only. The higher photocurrent densities of 3D nanostructured devices compared to planar one are attributed to the enhanced light trapping and increased surface area for photoelectrochemical water oxidation on the surface. The difference between valence and conduction bands of CuFe2O4 and α-Fe2O3 allows better separation of photogenerated electrons and holes at the CuFe2O4/ α-Fe2O3 interface which makes it more active for photoelectrochemical water splitting.

Fabrication of Highly Stable and Efficient PtCu Alloy Nanoparticles on Highly Porous Carbon for Direct Methanol Fuel Cells

Boosting the durability of Pt nanoparticles by controlling the composition and morphology is extremely important for fuel cells commercialization. We deposit the Pt-Cu alloy nanoparticles over high surface area carbon in different metallic molar ratios and optimize the conditions to achieve desired material. The novel bimetallic electro-catalyst {Pt-Cu/PC-950 (15:15%)} offers exceptional electrocatalytic activity when tested for both oxygen reduction reaction and methanol oxidation reactions. A high mass activity of 0.043 mA/μgPt (based on Pt mass) is recorded for ORR. An outstanding longevity of this electro-catalyst is noticed when compared to 20 wt % Pt loaded either on PC-950 or commercial carbon. The high surface area carbon support offers enhanced activity and prevents the nanoparticles from agglomeration, migration, and dissolution as evident by TEM analysis.

Titania supported MOF-199 derived Cu–Cu2O nanoparticles: highly efficient non-noble metal photocatalysts for hydrogen production from alcohol–water mixtures

Fabrication of cheap and efficient photocatalysts is pivotal for practical applications of solar energy devices. Here, we illustrate a novel trend in generating Cu–Cu2O nanoparticles over TiO2 for water splitting systems. Titanium(IV) isopropoxide was hydrolysed in the presence of various wt% of MOF-199 ([Cu3(BTC)2(H2O)3]n) to obtain TiO2–MOF-199 composite materials. These composite materials are then calcined at various temperatures in air to produce highly dispersed Cu–Cu2O nanoparticles over TiO2; these nanoparticles were tested as photocatalyts for hydrogen generation from alcohol–water mixtures. The photocatalyst 1 wt% Cu/TiO2-400 was found to exhibit a hydrogen production rate some 2.5 times higher than that of CuO prepared by conventional precipitation methods. The calcination temperature of the TiO2–MOF composite was found to affect the oxidation state of Cu and the photocatalytic activity, with an optimum performance achieved at 400 °C. Calcination beyond this temperature led to oxidation and agglomeration of Cu–Cu2O nanoparticles into larger CuO deposits, which reduce the H2 production activity (ca. 80%).

On the Synergism between Cu and Ni for Photocatalytic Hydrogen Production and their Potential as Substitutes of Noble Metals

A series of Cu(OH)2–Ni(OH)2/P25 photocatalysts was prepared by co‐deposition–precipitation (total metal loading ≈1 wt %) and their performance was evaluated for H2 production. Among this series, the 0.8 Cu(OH)2–0.2 Ni(OH)2/P25 photocatalyst demonstrated very high H2 production rates in 20 vol % ethanol/water and 5 vol % glycerol/water mixtures (10 and 22 mmol h−1 g−1, respectively). Detailed analyses based on reaction kinetics, photoluminescence, X‐ray photoelectron spectroscopy (XPS), and charge carrier scavenging suggest that both working catalysts are composed of Cu and Ni metals in their active phases. Cu0 is produced directly by the transfer of electrons from the conduction band of TiO2 to surface Cu(OH)2 nanoclusters, whereas Ni0 is formed indirectly through a process of gradual dissolution of Ni(OH)2 to yield aqueous Ni2+ owing to the acidic environment of the medium, followed by Ni2+ reduction by electrons from the TiO2 conduction band. The high rates of H2 production that match those obtained with noble metals can be explained owing to a considerably less negative ΔGo of Cu oxide formation when compared with that of Ni oxide formation and higher work function of Ni than that of Cu.

Suppression of methane formation during Fisher-Tropsch synthesis using manganese-cobalt oxide supported on H-5A zeolite as a catalyst

In Fischer-Tropsch synthesis reaction, methane formation is one of the side reactions which must be suppressed in order to get better catalytic selectivity for light olefins. In the present study, we have modified cobalt based Fischer-Tropsch catalyst and developed a process to minimize methane production, consequently to produce maximum yield of light olefins. Manganese-cobalt oxide supported on H-5A zeolite catalyst was synthesized using modified H-5A zeolite, to increase its surface acid sites. Increased acidity of zeolite plays a major part in the suppression of methane formation during the Fischer-Tropsch reaction. The modified zeolite results in the electronic modification of catalyst surface by creating new active catalytic sites. The results are compared with other supported catalysts along with unmodified zeolite. Appreciable reduction in methane formation is achieved on modified zeolite supported catalyst in comparison with unsupported catalyst.

Pd–Ag decorated g-C3N4 as an efficient photocatalyst for hydrogen production from water under direct solar light irradiation

A low visible light absorption efficiency and high recombination rate of photogenerated charge carriers are two major problems encountered in graphitic carbon nitride (g-C3N4) based photocatalysts for water splitting applications. In this work, Pd–Ag bimetallic and monometallic nanoparticles were decorated on graphitic carbon nitride by a simple chemical reduction method and evaluated for their ability to produce H2 during water splitting reactions. The physical and photophysical characteristics of the as-prepared Pd–Ag/g-C3N4 photocatalysts were studied by powder X-ray diffraction (PXRD), UV-visible diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and steady state photoluminescence (PL). The Pd0.7–Ag0.3/g-C3N4 photocatalyst with an overall metal loading of 1 wt% showed a very high H2 generation rate of 1250 μmol h−1 g−1, which is 1.5 and 5.7 times higher than those of the Pd/g-C3N4 and Ag/g-C3N4 photocatalysts, respectively. The high activity of the Pd–Ag/g-C3N4 photocatalyst was attributed to the inherent property of palladium metal to quench photogenerated electrons by the Schottky barrier formation mechanism and strong visible light absorption due to the characteristic surface plasmon resonance (SPR) of silver nanoparticles along with the absorption of g-C3N4.

Acid base co-crystal converted into porous carbon material for energy storage devices

A simple and facile method is adopted for the synthesis of pure and catalyst free carbon material for supercapacitor applications. In a co-crystal synthesis, the precursors (isophthalic acid and a base, 4,4′-bipyridine) are arranged in regular pattern, followed by carbonization at 600 °C under an inert atmosphere to produce pure carbon material, CIN-600. The obtained sample is characterized by many techniques, such as powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and gas adsorption analysis. The gas adsorption and microscopic analysis demonstrated the high porosity of the carbon sample and its irregular geometry. Owing to the excellent porosity and electrical conducting properties, CIN-600 showed enhanced capacitive performance when used as an electrode material in electric double layer capacitors. The specific capacitance of the sample was ca.181.3 F g−1 at 2 mV s−1 and maintained 91.3% of its initial capacitance in a long-term cycling test.

Nanotextured Spikes of α-Fe2O3/NiFe2O4 Composite for Efficient Photoelectrochemical Oxidation of Water

We demonstrate for the first time the application of p-NiFe2O4/n-Fe2O3 composite thin films as anode materials for light-assisted electrolysis of water. The p-NiFe2O4/n-Fe2O3 composite thin films were deposited on planar fluorinated tin oxide (FTO)-coated glass as well as on 3D array of nanospike (NSP) substrates. The effect of substrate (planar FTO and 3D-NSP) and percentage change of each component (i.e., NiFe2O4 and Fe2O3) of composite was studied on photoelectrochemical (PEC) water oxidation reaction. This work also includes the performance comparison of p-NiFe2O4/n-Fe2O3 composite (planar and NSP) devices with pure hematite for PEC water oxidation. Overall, the nanostructured p-NiFe2O4/n-Fe2O3 device with equal molar 1:1 ratio of NiFe2O4 and Fe2O3 was found to be highly efficient for PEC water oxidation as compared with pure hematite, 1:2 and 1:3 molar ratios of composite. The photocurrent density of 1:1 composite thin film on planar substrate was equal to 1.07 mA/cm2 at 1.23 VRHE, which was 1.7 times higher current density as compared with pure hematite device (0.63 mA/cm2 at 1.23 VRHE). The performance of p-NiFe2O4/n-Fe2O3 composites in PEC water oxidation was further enhanced by their deposition over 3D-NSP substrate. The highest photocurrent density of 2.1 mA/cm2 at 1.23 VRHE was obtained for the 1:1 molar ratio p-NiFe2O4/n-Fe2O3 composite on NSP (NF1-NSP), which was 3.3 times more photocurrent density than pure hematite. The measured applied bias photon-to-current efficiency (ABPE) value of NF1-NSP (0.206%) was found to be 1.87 times higher than that of NF1-P (0.11%) and 4.7 times higher than that of pure hematite deposited on FTO-coated glass (0.044%). The higher PEC water oxidation activity of p-NiFe2O4/n-Fe2O3 composite thin film as compared with pure hematite is attributed to the Z-path scheme and better separation of electrons and holes. The increased surface area and greater light absorption capabilities of 3D-NSP devices result in further improvement in catalytic activities.

Novel hetero-bimetallic coordination polymer as a single source of highly dispersed Cu/Ni nanoparticles for efficient photocatalytic water splitting

A new strategy for depositing highly dispersed Cu and Ni nanoparticles on the surface of TiO2 from a single source is demonstrated for photocatalytic hydrogen production. We used a newly synthesized cyanide-bridged hetero-bimetallic coordination polymer [{CuII(4,4′-dipy)2}{Ni(CN)4}]n·0.7(C2H6O2).1.6(H2O) (CP-1) (4,4′-dipy = 1,3-di(4-pyridyl)propane) as a single-source precursor of Cu–Ni nanoparticles. The structure of CP-1 was established by single-crystal X-ray diffraction analysis; CP-1 crystallizes in the monoclinic space group C2/c with β = 111.67(3)°. CP-1/TiO2 composites containing different weight percentages of CP-1 were achieved by hydrolyzing titanium isopropoxide in the presence of CP-1. Highly dispersed Cu and Ni nanoparticles were deposited on TiO2 by the calcination of the CP-1/TiO2 composites at different temperatures (420 °C, 470 °C and 520 °C) in air followed by reduction in H2/Ar atmosphere at 470 °C for 2 h. XRD, DRS/UV–Vis, TEM, Cu/Ni 2p XPS, and photoluminescence spectroscopy demonstrated the presence of CuO/Cu0 and NiO/Ni0 as active co-catalysts on the surface of TiO2. The 1 wt% Cu–Ni/TiO2-470 photocatalyst showed the maximum H2 production activity of 8.5 mmol h−1 g−1 in a glycerol/water mixture (20 vol%). The results are anticipated to direct the future development of efficient, low-cost and noble metal-free semiconductor photocatalysts for solar H2 production.