The recent advances in electrocatalysis for oxygen reduction reaction (ORR) for proton exchange membrane fuel cells (PEMFCs) are thoroughly reviewed. This comprehensive Review focuses on the low- and non-platinum electrocatalysts including advanced platinum alloys, core–shell structures, palladium-based catalysts, metal oxides and chalcogenides, carbon-based non-noble metal catalysts, and metal-free catalysts. The recent development of ORR electrocatalysts with novel structures and compositions is highlighted. The understandings of the correlation between the activity and the shape, size, composition, and synthesis method are summarized. For the carbon-based materials, their performance and stability in fuel cells and comparisons with those of platinum are documented. The research directions as well as perspectives on the further development of more active and less expensive electrocatalysts are provided.

http://repository.ust.hk/ir/bitstream/1783.1-77094/1/acs.chemrev.5b00462_withlink.pdf

Recent Advances in Electrocatalysts for Oxygen Reduction Reaction

Graphene and related two-dimensional crystals and hybrid systems showcase several key properties that can address emerging energy needs, in particular for the ever growing market of portable and wearable energy conversion and storage devices. Graphene's flexibility, large surface area, and chemical stability, combined with its excellent electrical and thermal conductivity, make it promising as a catalyst in fuel and dye-sensitized solar cells. Chemically functionalized graphene can also improve storage and diffusion of ionic species and electric charge in batteries and supercapacitors. Two-dimensional crystals provide optoelectronic and photocatalytic properties complementing those of graphene, enabling the realization of ultrathin-film photovoltaic devices or systems for hydrogen production. Here, we review the use of graphene and related materials for energy conversion and storage, outlining the roadmap for future applications.

Graphene, related two-dimensional crystals, and hybrid systems for energy conversion and storage

日本物理学会誌及びJournal of the Physical Society of Japanの月刊について

Annual review of condensed matter physics

Review: Carbon nanotube based electrochemical sensors for biomolecules.

We have prepared semiconducting carbon nanoparticle polyimide composite thin film with spatially distributed localized energy states exhibiting three-dimensional variable range hopping electron transport. Applied strain (compression or extensional) introduces proportional variations in the spacing between these energy states, as demonstrated in the linear variation of measured electrical resistance. The electromechanical sensitivity is the same in both deformation modes due to this underlying operating mechanism, enabling quantitative measurement of torsional deformations also. Electrical responses across all deformation modes remained in phase with applied strain indicating negligible hysteresis and an ability to operate over a wide strain ranges up to 40 000 microstrains.

Enhanced electromechanical response of nonpercolating polymer-nanoparticle composite films

Magnetocaloric effect in single-crystalline Nd1−xSrxMnO3 (x=0.3, 0.5)

https://iopscience.iop.org/article/10.1088/2399-6528/aab39f/pdf

Flux pinning and improved critical current density in superconducting boron doped diamond films

We report the experimental observation of spin reorientation in the double perovskite Ho$_2$FeCoO$_6$. The magnetic phase transitions in this compound are characterized and studied through magnetization and specific heat, and the magnetic structures are elucidated by neutron powder diffraction. Two magnetic phase transitions are observed in this compound - one at $T_\mathrm{N1} \approx$ 250~K, from paramagnetic to antiferromagnetic, and the other at $T_\mathrm{N2} \approx$ 45~K, from a phase with mixed magnetic structures to a single phase through a spin reorientation process. The magnetic structure in the temperature range 200~K - 45~K is a mixed phase of the irreducible representations $\Gamma_1$ and $\Gamma_3$, both of which are antiferromagnetic. The phase with mixed magnetic structures that exists in Ho$_2$FeCoO$_6$ gives rise to a large thermal hysteresis in magnetization that extends from 200~K down to the spin reorientation temperature. At $T_\mathrm{N2}$, the magnetic structure transforms to $\Gamma_1$. Though long-range magnetic order is established in the transition metal lattice, it is seen that only short-range magnetic order prevails in Ho$^{3+}$ - lattice. Our results should motivate further detailed studies on single crystals in order to explore spin reorientation process, spin switching and the possibility of anisotropic magnetic interactions giving rise to electric polarization in Ho$_2$FeCoO$_6$.

Spin reorientation and disordered rare earth magnetism in Ho$_2$FeCoO$_6$

We report electron spin resonance measurements in single crystalline Nd0.7Sr0.3MnO3 that provide evidence for the existence of spin–lattice correlated clusters above and below TC (= 205 K). The linewidth of the paramagnetic spectrum indicates the presence of strong electron–phonon interaction rather than the spin only interaction seen in other manganites. The gradual increase observed in the g value above TC is attributed to the presence of orbital correlations. The observation of ferromagnetic resonance (FMR) spectra only below 185 K (TC = 205 K) and noisy features in the FMR spectra above 140 K are ascribed to the strong competition between localization due to lattice distortions and delocalization of charge carriers. The magnetocrystalline anisotropy of the sample splits the FMR line into two below 185 K. An additional splitting observed in the FMR line is attributed to the existence of spin–lattice correlated (insulating) clusters within the ferromagnetic (metallic) phase. The influence of these clusters on the spin dynamics above and below TC is discussed.

K. Sethupathi

Papers

Enhanced electromechanical response of nonpercolating polymer-nanoparticle composite films

Magnetocaloric effect in single-crystalline Nd1−xSrxMnO3 (x=0.3, 0.5)

Flux pinning and improved critical current density in superconducting boron doped diamond films

Spin reorientation and disordered rare earth magnetism in Ho$_2$FeCoO$_6$

ESR study of spin–lattice correlated clusters in single crystalline Nd0.7Sr0.3MnO3