Recently, PtM (M = Fe, Ni, Co, Cu, etc.) intermetallic compounds have been highlighted as promising candidates for oxygen reduction reaction (ORR) catalysts. In general, to form those intermetallic compounds, alloy phase nanoparticles are synthesized and then heat-treated at a high temperature. However, nanoparticles easily agglomerate during the heat treatment, resulting in a decrease in electrochemical surface area (ECSA). In this study, we synthesized Pt-Fe alloy nanoparticles and employed carbon coating to protect the nanoparticles from agglomeration during heat treatment. As a result, PtFe L1 structure was obtained without agglomeration of the nanoparticles; the ECSA of Pt-Fe alloy and intermetallic PtFe/C was 37.6 and 33.3 m g, respectively. PtFe/C exhibited excellent mass activity (0.454 A mg) and stability with superior resistances to nanoparticle agglomeration and iron leaching. Density functional theory (DFT) calculation revealed that, owing to the higher dissolution potential of Fe atoms on the PtFe surface than those on the Pt-Fe alloy, PtFe/C had better stability than Pt-Fe/C. A single cell fabricated with PtFe/C showed higher initial performance and superior durability, compared to that with commercial Pt/C. We suggest that PtM chemically ordered electrocatalysts are excellent candidates that may become the most active and durable ORR catalysts available.

Layered cobalt (oxy)hydroxides have received much attention as cost-effective and efficient catalysts for the oxygen evolution reaction (OER) for electrochemical water splitting. Doping with guest cations possessing different oxidation states such as Ag can change the chemistry of conventional transition metal oxides and hydroxides, generating unexpected electrocatalytic performances. However, Ag dopants have been found to easily segregate at the surface of electrocatalysts, which induces deactivation. Here, we fabricated Ag-doped CoOOH nanosheet arrays using electrochemical deposition, followed by a simple electrochemical diffusion approach. Surprisingly, we revealed, through atom probe tomography (APT), secondary ion mass spectroscopy (SIMS), and energy-dispersive spectroscopy (EDS) that Ag atoms are homogeneously distributed without any detectable segregation. The Ag-doped CoOOH exhibits enhanced OER performance in terms of overpotential, both experimentally (256 mV) and theoretically (60 mV). The homogeneously distributed Ag dopants facilitate the phase transformation from Co(OH) 2 to the active phase of CoOOH. Calculations show that Ag doping enhances phase stability of CoOOH and exposed Ag dopants act as active sites by releasing −OH adsorbates.

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Heavy-alkali post-deposition treatments (PDTs) utilizing Cs or Rb has become an indispensable step in producing high-performance Cu(In,Ga)Se 2 (CIGS) solar cells. However, full understanding of the mechanism behind the improvements of device performance by heavyalkali treatments, particularly in terms of potential modification of defect characteristics, has not been reached yet. Here, we present an extensive study on the effects of CsF-PDT on material properties of CIGS absorbers and the performance of the final solar devices. Incorporation of an optimized concentration of Cs into CIGS resulted in a significant improvement of the device efficiency from 15.9 to 18.4% mainly due to an increase in the open-circuit voltage by 50 mV. Strong segregation of Cs at the front and rear interfaces as well as along grain boundaries of CIGS was observed via high-resolution chemical analysis such as atomic probe tomography. The study of defect chemistry using photoluminescence and capacitance-based measurements revealed that both deep-level donor-like defects such as V Se and In Cu and deep-level acceptor-like defects such as V In or Cu In are passivated by CsF-PDT, which contribute to an increased hole concentration. Additionally, it was found that CsF-PDT induces a slight change in the energetics of V Cu , the most dominant point defect that is responsible for the p-type conductivity of CIGS.

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The worldwide developments of electric vehicles, as well as large-scale or grid-scale energy storage to compensate the intermittent nature of renewable energy generation has generated a surge of interest in...

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