Pradeep Haldar

Titanium nitride nanoparticles based electrocatalysts for proton exchange membrane fuel cells

Titanium nitride nanoparticles act as a catalyst support material for proton exchange membrane fuel cells showing higher catalytic performance than conventional platinized carbon electrocatalysts.

Flux pinning enhancement in YBa2Cu3O7−x films with BaSnO3 nanoparticles

Nanoparticles of BaSnO3 were incorporated into YBa2Cu3O7?x (YBCO) films on LaAlO3 substrates for magnetic flux pinning enhancements. More than an order of magnitude improvement in the high field magnetization Jc at 6?T at 77?K was observed as compared to regular YBCO films. The irreversibility field (Hirr) was increased to 8.5?T at 77?K and to 13.4?T at 65?K. The in-field transport current measurements confirmed an order of magnitude improvement in high fields. The angular dependence of the Jc data at 1?T showed that is 1.3 times higher than indicating the presence of c-axis correlated defects. Transmission electron microscopy studies revealed the presence of a large density of uniformly distributed ~10?nm sized BaSnO3 precipitates and strain fields around them. A dual sector pulsed laser deposition target is used to produce the films, thus eliminating reactions between BaSnO3 and YBCO during the target preparation stage, but may allow the BaSnO3 to react locally and create defects that act as pinning centres.

Enhancement in critical current density of Bi‐Pb‐Sr‐Ca‐Cu‐O tapes by thermomechanical processing: Cold rolling versus uniaxial pressing

Critical current densities up to 24 000 A/cm2 (Ic∼23.6 A) at 77 K, zero field, have been measured in short tape samples of silver‐sheathed Bi‐Pb‐Sr‐Ca‐Cu‐O superconductors made by the powder‐in‐tube technique. These samples carried 3000 A/cm2 at 1 T and 1000 A/cm2 at 2 T, also at liquid‐nitrogen temperature. A repeated cold work (rolling and pressing) together with an intermediate heat treatment were required to achieve these properties. Without the pressing, tapes were made with Jc’s as high as 15 000 A/cm2 at 77 K, zero field. The role of uniaxial pressing as compared to rolling is discussed and its implications to long length conductor fabrication described.

Synchrotron x‐ray scattering measurements of bulk structural properties in superconducting (Bi,Pb)2Sr2Ca2Cu3O10–Ag tapes

The structural properties of superconducting (Bi,Pb)2Sr2Ca2Cu3O10–Ag (2223) tapes have been measured using synchrotron x‐ray scattering techniques. The x‐ray photon energy was tuned just below the silver K absorption edge so the penetration depth was large, which allowed the measurements to be performed in a transmission geometry without removing the silver cladding. Analysis of the peaks in 2θ scans indicates that residual (Bi,Pb)2Sr2CaCu2O8 (2212) superconductor starting material is present in all samples studied. The amount of 2212 varied widely among the tapes, and was not homogeneous along the length of each individual tape. Residual 2212 content increased near the ends of most samples, suggesting that 2223 phase development is sensitive to whether the superconducting material is encased in silver or not. The bulk c‐axis alignment was measured in ∼100 mono‐ and multifilament samples, and correlations between c‐axis alignment and current carrying capacity at 77 K were found. Multifilament samples gene...

Highly Active Carbon Supported Core-Shell PtNi@Pt Nanoparticles for Oxygen Reduction Reaction

A carbon supported core-shell PtNi@Pt nanoparticle catalyst was synthesized through a two-step solution-phase reduction method, and it demonstrated a 5.4 times higher specific activity to an oxygen reduction reaction than a conventional Pt/C catalyst by using a rotating disk electrode in a three-compartment electrochemical cell, which could be attributed to the modified electronic structure of the Pt surface layer.

Transport critical current densities of silver clad Bi‐Pb‐Sr‐Ca‐Cu‐O tapes at liquid helium and hydrogen temperatures

Using improved processing conditions, we have succeeded in increasing the transport critical current density (Jc) of powder‐in‐tube fabricated silver sheathed Bi‐Pb‐Sr‐Ca‐Cu‐O superconducting tapes. Jc values at zero field now exceed 1.6×105 A/cm2 (Ic∼164 A) at 4.2 K and 1.3×105 A/cm2 (Ic∼133 A) at 20.2 K for short tape samples. At 77 K the same samples exhibit values greater than 3.0×104 A/cm2 (Ic∼32 A). They continue to carry 6.5×104 A/cm2 at 4.2 K and 4.8×104 A/cm2 at 20.2 K with applied magnetic fields as high as 20 T. Long lengths of tape were also fabricated and measured by winding the composites into small spiral or pancake coils. The small pancake coils carried 4.8×104 A/cm2 at 4.2 K and 5.2×103 A/cm2 at 77 K, zero field. More recently, 1 m lengths have been measured with Jc’s as high as 1.0×104 A/cm2 at 77 K, zero field. Detailed transport measurements at liquid helium and hydrogen temperatures with applied magnetic fields up to 20 T are reported for short and long lengths of monocore tapes.

Processing high critical current density Bi-2223 wires and tapes

Considerable progress has been made in fabricating (Bi,Pb)2Sr2Ca2Cu3O10 in high-Tc superconductor wires or tapes with high critical current densities that are attractive for electric power and high-field magnet applications. The powder-in-tube technique appears to be useful for making silver-clad Bi-2223 composites. This article discusses the processing and the excellent superconducting properties of the resulting wires and tapes.

Multifilament NbTi with artificial pinning centers: The effect of alloy and pin material on the superconducting properties

Low‐temperature superconductors containing artificial pinning centers (APC) have produced record critical current densities in NbTi at magnetic fields below 4 T and promise further improvements at these and higher fields. Peak current densities are achieved when pinning center spacings are matched to spacings of the flux line lattice at the field of operation. The enhancement of Jc through inclusion of artificial pinning materials is accompanied by reduction in Tc and Hc2 through proximity effects. We find that the choice of the superconducting alloy as well as the pin material has marked effect on both the characteristic pinning force Fp and the critical magnetic field Hc2.

Limiting factors for critical current densities in Bi2Sr2Ca2Cu3O10‐Ag composite superconducting tapes at elevated temperatures

Detailed measurements of I‐V curves at 4.2, 65, and 77 K as a function of applied magnetic field for two Bi(2:2:2:3)/Ag tapes, having critical current densities Jc of ∼1 and ∼2×104 A/cm2 (at 77 K and 0 T), revealed that (1) the primary limiting factor for the transport critical current densities in these tapes is the presence of a large fraction of weak and/or nonsuperconducting grain boundaries; (2) the observed dissipative voltages are due, however, mostly to the motion of the magnetic vortices in the grains; and (3) the E‐J curves are well described by an expression, E∼exp[−(J0/J)μ], rather than the commonly used power law, i.e., E∼Jn, where μ, J0, and n are constants.

Alternating‐current losses in silver‐sheathed (Bi,Pb)2Sr2Ca2Cu3O10 tapes II: Role of interfilamentary coupling

ac losses at 60 Hz have been measured for silver‐sheathed (Bi,Pb)2Sr2Ca2Cu3O10 multifilamentary tapes at 27 and 77 K to investigate the role of interfilamentary coupling. The results are qualitatively well described by the use of the concept of the critical coupling length lc. Further, it is shown that to obtain effective reduction of the coupling loss, a very small twist pitch length (≪1 cm) as well as a substantial reduction in the filament thickness are required for an applied ac field of, for example, 100 rms A/cm at 77 K.