Iridium–nickel
(Ir–Ni) and iridium–cobalt
(Ir–Co) nanowires have been synthesized by galvanic displacement
and studied for their potential to increase the performance and durability
of electrolysis systems. Performances of Ir–Ni and Ir–Co
nanowires for the oxygen evolution reaction (OER) have been measured
in rotating disk electrode half-cells and single-cell electrolyzers
and compared with commercial baselines and literature references.
The nanowire catalysts showed improved mass activity, by more than
an order of magnitude compared with commercial Ir nanoparticles in
half-cell tests. The nanowire catalysts also showed greatly improved
durability, when acid-leached to remove excess Ni and Co. Both Ni
and Co templates were found to have similarly positive impacts, although
specific differences between the two systems are revealed. In single-cell
electrolysis testing, nanowires exceeded the performance of Ir nanoparticles
by 4–5 times, suggesting that significant reductions in catalyst
loading are possible without compromising performance.
For
the first time, extended nanostructured catalysts are demonstrated
with both high specific activity (>6000 μA cm
Pt
–2
at 0.9 V) and high surface areas (>90 m
2
g
Pt
–1
). Platinum–nickel
(Pt—Ni)
nanowires, synthesized by galvanic displacement, have previously produced
surface areas in excess of 90 m
2
g
Pt
–1
, a significant breakthrough in and of itself for extended surface
catalysts. Unfortunately, these materials were limited in terms of
their specific activity and durability upon exposure to relevant electrochemical
test conditions. Through a series of optimized postsynthesis steps,
significant improvements were made to the activity (3-fold increase
in specific activity), durability (21% mass activity loss reduced
to 3%), and Ni leaching (reduced from 7 to 0.3%) of the Pt—Ni
nanowires. These materials show more than a 10-fold improvement in
mass activity compared to that of traditional carbon-supported Pt
nanoparticle catalysts and offer significant promise as a new class
of electrocatalysts in fuel cell applications.
Solid metal oxides for carbon capture exhibit reduced adsorption capacity following high-temperature exposure, due to surface area reduction by sintering. Furthermore, only low-coordinate corner/edge sites on the thermodynamically stable (100) facet display favorable binding toward CO, providing inherently low capacity. The (111) facet, however, exhibits a high concentration of low-coordinate sites. In this work, MgO(111) nanosheets displayed high capacity for CO, as well as a ∼65% increase in capacity despite a ∼30% reduction in surface area following sintering (0.77 mmol g @ 227 m g vs 1.28 mmol g @ 154 m g). These results, unique to MgO(111), suggest intrinsic differences in the effects of sintering on basic site retention. Spectroscopic and computational investigations provided a new structure-activity insight: the importance of high-temperature activation to unleash the capacity of the polar (111) facet of MgO. In summary, we present the first example of a faceted sorbent for carbon capture and challenge the assumption that sintering is necessarily a negative process; here we leverage high-temperature conditions for facet-dependent surface activation.
The
development of adsorbents with molecular precision offers a
promising strategy to enhance storage of hydrogen and methaneconsidered
the fuel of the future and a transitional fuel, respectivelyand
to realize a carbon-neutral energy cycle. Herein we employ a postsynthetic
modification strategy on a robust metal–organic framework (MOF),
MFU-4l, to boost its storage capacity toward these clean energy gases.
MFU-4l-Li displays one of the best volumetric deliverable hydrogen
capacities of 50.2 g L–1 under combined temperature
and pressure swing conditions (77 K/100 bar → 160 K/5 bar)
while maintaining a moderately high gravimetric capacity of 9.4 wt
%. Moreover, MFU-4l-Li demonstrates impressive methane storage performance
with a 5–100 bar usable capacity of 251 cm3 (STP)
cm–3 (0.38 g g–1) and 220 cm3 (STP) cm–3 (0.30 g g–1) at 270 and 296 K, respectively. Notably, these hydrogen and methane
storage capacities are significantly improved compared to those of
its isoreticular analogue, MFU-4l, and place MFU-4l-Li among the best
MOF-based materials for this application.
Hydrogen induced flexibility in MOFs can be leveraged to increase useable gas storage capacities. Here hydrogen adsorption isothermal and in situ powder neutron diffraction measurements combine to reveal the mechanism driving flexibility in ZIF-7.
Copper(II) formate is efficiently incorporated into the pores of a 2D imine-based covalent organic framework (COF) via coordination with the phenol and imine groups. The coordinated metal ion is then reduced to Cu(I) with a thermal treatment that evolves CO 2 . After loading with hydrogen gas, the majority of H 2 desorbs from the coordinatively saturated Cu(II) COF at temperatures < −100 °C. However, the activated Cu(I) COF retains adsorbed H 2 above room temperature. Adsorption/ desorption of H 2 was highly reversible. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) strongly supports a molecular hydrogen interaction with Cu(I). A Kissinger analysis of variable ramp rate desorption experiments estimates the enthalpy of H 2 desorption from Cu(I) at 15 kJ mol −1 . The results represent an advance toward practical H 2 storage and delivery in a lightweight, stable, and highly versatile material.
Recent advances in theoretical structure prediction methods and high-throughput computational techniques are revolutionizing experimental discovery of the thermodynamically stable inorganic materials. Metastable materials represent a new frontier for studies, since even simple binary non ground state compounds of common elements may be awaiting discovery. However, there are significant research challenges related to non-equilibrium thin film synthesis and crystal structure predictions, such as small strained crystals in the experimental samples and energy minimization based theoretical algorithms. Here we report on experimental synthesis and characterization, as well as theoretical first-principles calculations of a previously unreported mixed-valent binary tin nitride. Thin film experiments indicate that this novel material is Ndeficient SnN with tin in the mixed II/IV valence state and a small low-symmetry unit cell. Theoretical calculations suggest that the most likely crystal structure has the space group 2 (SG2) related to the distorted delafossite (SG166), which is nearly 0.1 eV/atom above the ground state SnN polymorph. This observation is rationalized by the structural similarity of the SnN distorted delafossite to the chemically related Sn 3 N 4 spinel compound, which provides a fresh scientific insight into the reasons for growth of polymorphs of the metastable material. In addition to reporting on the discovery of the simple binary SnN compound, this paper illustrates a possible way of combining a wide range of advanced characterization techniques with the first-principle property calculation methods, to elucidate the most likely crystal structure of the previously unreported metastable materials.
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