Cathode catalysts without platinum group metals (PGMs) or carbon supports can reduce the price of polymer electrolyte fuel cells in automobiles, making them commercially competitive. In this paper, an inexpensive and PGM-free catalyst-amorphous nitrogen-doped TiO 2-shell on TiN-core-was synthesized without carbon support. While existing PGM-free all-oxide catalysts without carbon support have shown moderate current densities (at the order of μA/cm 2), the current density of this new catalyst is three orders of magnitude higher. Replacing commercial carbon support by hydrothermally synthesized Ti 4 O 7 significantly enhanced the activity to be close to that of carbon-supported platinum. Although its conductivity and surface area were not sufficient for an accurate evaluation of its activity, these new results demonstrate the possibility of high-performance non-PGM catalysts without carbon supports.

The ORR active rutile-shell successfully protected the TiN-core without altering the mechanism during 20 000 cycles in acidic media.

No abstract

To understand the effect of bandgap grading on carrier recombination for Cu(In,Ga)Se 2 (CIGS)-based solar cells in detail, samples with different bandgaps at the CIGS surface were fabricated by changing the Ga/(Ga + In) (GGI) ratio from 0.4 to 0 at the third stage of the conventional threestage growth process. Optoelectronic characterizations, such as photoluminescence, temperature-dependent open-circuit voltage measurement and light-intensity-dependent current-voltage measurement, indicate that the photo-generated carriers move rapidly towards the location of the bandgap minimum, and the carrier recombination occurs mainly at this location. From simulation using a one-dimensional solar cell capacitance simulator (SCAPS-1D), a single-grade sample with the smallest bandgap on the surface of CIGS showed high recombination current at the surface, while the location of the maximum recombination current moved from the surface to the bulk for double-grade samples. This study suggests that controlling the bandgap grading is one way of suppressing recombination at the interface in CIGS-based solar cells.

Single crystal Mo thin films are successfully grown on single-crystal sapphire {0001} substrates using a newly developed two-step sputtering method. Cu(In 1-x ,Ga x )Se 2 (CIGS) thin films are then epitaxially grown on the Mo thin films by three-stage co-evaporation. Following that, a CdS buffer layer is deposited on the epitaxial (epi)-CIGS thin films by a chemical bath deposition (CBD) method, leading to the overall epitaxial relations such as CdS{111}// CIGS{112}//MoSe 2 {0001}//Mo{110}//sapphire {0001}. The Cd-diffusion into the CIGS occurs to approximately 30 nm from the CIGS/CdS interface boundary together with depleted Cu at the CIGS surface region. This suggests that Cd diffuses through Cu vacancies in the intra-grain rather than at the grain boundaries. Two distinct solar cells are fabricated using epi-and polycrystalline (poly)-CIGS thin films deposited on sapphire substrates in the same deposition run. The open-circuit-voltage (V OC ) of epi-CIGS solar cell is found to be higher than poly-CIGS solar cell. The net carrier concentration (N CV ) derived from the capacitance-voltage (C-V) measurements of epi-CIGS solar cell is 3.5 times higher than poly-CIGS solar cell, suggesting one of the causes of higher V OC . This large difference in the N CV is discussed based on the results of low-temperature photoluminescence measurements.