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Chromium versus Aluminum: Impact of Nickel Alloy Composition and Interfacial Kinetics on High-Temperature Passivating Oxide Formation
High-temperature corrosion resistance depends critically on the formation of a passivating surface oxide, which is highly sensitive to alloy composition and structure. Such details often elude experimental investigation, and simplified analytical models fail to provide a truly chemical view of passivating oxide evolution. Here, we explicitly compare the fundamental chemistry of Cr and Al as prototypical passivating elements in Ni alloys by directly simulating competing reaction and diffusion processes within the oxide film using kinetic Monte Carlo and density functional theory. We find that the origin and expression of passivating behavior during early-stage thermal oxidation are qualitatively different between the two alloy systems. Ni–Cr alloys feature a sudden onset of passivation associated with a sharp phase transition upon Cr enrichment that directly couples oxidation kinetics to phase transformation behavior. In contrast, Ni–Al alloys display more continuous oxide phase variation with Al enrichment, ultimately resulting in a lower composition threshold for passivation and a thinner passivating layer. In addition, we elucidate the nonobvious role of metal exchange within the alloy near the oxide boundary, which fundamentally alters film composition and passivating behavior. Furthermore, our results have key implications for engineering improved corrosion-resistant alloys, both in terms of compositional variation and processing.
Reaction mechanism and kinetics for CO 2 reduction on nickel single atom catalysts from quantum mechanics
Experiments have shown that graphene-supported Ni-single atom catalysts (Ni-SACs) provide a promising strategy for the electrochemical reduction of CO 2 to CO, but the nature of the Ni sites (Ni-N 2 C 2 , Ni-N 3 C 1 , Ni-N 4 ) in Ni-SACs has not been determined experimentally. Here, we apply the recently developed grand canonical potential kinetics (GCP-K) formulation of quantum mechanics to predict the kinetics as a function of applied potential (U) to determine faradic efficiency, turn over frequency, and Tafel slope for CO and H 2 production for all three sites. We predict an onset potential (at 10 mA cm –2 ) U onset = –0.84 V (vs. RHE) for Ni-N 2 C 2 site and U onset = –0.92 V for Ni-N 3 C 1 site in agreement with experiments, and U onset = –1.03 V for Ni-N 4 . We predict that the highest current is for Ni-N 4 , leading to 700 mA cm –2 at U = –1.12 V. To help determine the actual sites in the experiments, we predict the XPS binding energy shift and CO vibrational frequency for each site.
Effect of the grain arrangements on the thermal stability of polycrystalline nickel-rich lithium-based battery cathodes
One of the most challenging aspects of developing high-energy lithium-based batteries is the structural and (electro)chemical stability of Ni-rich active cathode materials at thermally-abused and prolonged cell cycling conditions. Here, we report in situ physicochemical characterizations to improve the fundamental understanding of the degradation mechanism of charged polycrystalline Ni-rich cathodes at elevated temperatures (e.g., ≥ 40 °C). Using multiple microscopy, scattering, thermal, and electrochemical probes, we decouple the major contributors for the thermal instability from intertwined factors. Our research work demonstrates that the grain microstructures play an essential role in the thermal stability of polycrystalline lithium-based positive battery electrodes. We also show that the oxygen release, a crucial process during battery thermal runaway, can be regulated by engineering grain arrangements. Furthermore, the grain arrangements can also modulate the macroscopic crystallographic transformation pattern and oxygen diffusion length in layered oxide cathode materials.
Characterization of paramagnetic states in an organometallic nickel hydrogen evolution electrocatalyst
Abstract Significant progress has been made in the bioinorganic modeling of the paramagnetic states believed to be involved in the hydrogen redox chemistry catalyzed by [NiFe] hydrogenase. However, the characterization and isolation of intermediates involved in mononuclear Ni electrocatalysts which are reported to operate through a Ni I/III cycle have largely remained elusive. Herein, we report a Ni II complex (NCHS2)Ni(OTf)2, where NCHS2 is 3,7-dithia-1(2,6)-pyridina-5(1,3)-benzenacyclooctaphane, that is an efficient electrocatalyst for the hydrogen evolution reaction (HER) with turnover frequencies of ~3,000 s −1 and a overpotential of 670 mV in the presence of trifluoroacetic acid. This electrocatalyst follows a hitherto unobserved HER mechanism involving C-H activation, which manifests as an inverse kinetic isotope effect for the overall hydrogen evolution reaction, and Ni I /Ni III intermediates, which have been characterized by EPR spectroscopy. We further validate the possibility of the involvement of Ni III intermediates by the independent synthesis and characterization of organometallic Ni III complexes.
Author Correction: Limits to the strain engineering of layered square-planar nickelate thin films
In the Acknowledgements section of this article the grant number relating to NSF was incorrectly given as DMR 2045826 and should have been DMR-2045826. The original article has been corrected.
Interlayer pairing in bilayer nickelates
The discovery of T c ~ 80 K superconductivity in pressurized La 3 Ni 2 O 7 has launched a new platform to study high-temperature superconductivity. Using non-perturbative dynamic cluster approximation quantum Monte Carlo calculations, we characterize the magnetic and superconducting pairing behavior of a realistic bilayer two-orbital Hubbard-Hund model of this system that describes the relevant Ni e g states with physically relevant interaction strengths. We find a leading s ± superconducting instability in this model at a temperature T ~ 100 K close to the experimentally observed T c . Analyzing the orbital and spatial structure of the effective pairing interaction giving rise to this state reveals that the interaction predominantly acts between local interlayer pairs of the $d_{3z^2-r^2}$ orbital. By correlating the strength of the interaction with that of the magnetic spin fluctuations we show that it is driven by strong interlayer spin-fluctuations arising from the $d_{3z^2-r^2}$ orbital. These results provide first-time non-perturbative evidence supporting the picture that a simple single-orbital bilayer Hubbard model for the Ni $d_{3z^2-r^2}$ orbital provides an excellent low-energy effective description of the superconducting behavior of La 3 Ni 2 O 7 .
High-nickel layered oxide cathodes for lithium-based automotive batteries
Not provided.
Amorphous nickel hydroxide shell tailors local chemical environment on platinum surface for alkaline hydrogen evolution reaction
In analogy to natural enzymes, an elaborated design of catalytic systems with a specifically tailored local chemical environment could substantially improve reaction kinetics, effectively combat catalyst poisoning effect and boost catalyst lifetime under unfavourable reaction conditions. Here we report a unique design of ‘Ni(OH) 2 -clothed Pt-tetrapods’ with an amorphous Ni(OH) 2 shell as a water dissociation catalyst and a proton conductive encapsulation layer to isolate the Pt core from bulk alkaline electrolyte while ensuring efficient proton supply to the active Pt sites. This design creates a favourable local chemical environment to result in acidic-like hydrogen evolution reaction kinetics with a lowest Tafel slope of 27 mV per decade and a record-high specific activity and mass activity in alkaline electrolyte. The proton conductive Ni(OH) 2 shell can also effectively reject impurity ions and retard the Oswald ripening, endowing a high tolerance to solution impurities and exceptional long-term durability that is difficult to achieve in the naked Pt catalysts. Furthermore, the markedly improved hydrogen evolution reaction activity and durability in an alkaline medium promise an attractive catalyst material for alkaline water electrolysers and renewable chemical fuel generation.
Uncovering a superfamily of nickel-dependent hydroxyacid racemases and epimerases
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Multimodal electrochemistry coupled microcalorimetric and X-ray probing of the capacity fade mechanisms of Nickel rich NMC – progress and outlook
Combining calorimetry with hard and soft X-ray characterization elucidates bulk and surface phenomena responsible for capacity fade in LiNi 0.8 Mn 0.1 Co 0.1 O 2 cathodes.
Nickel foam supported porous copper oxide catalysts with noble metal-like activity for aqueous phase reactions
Contiguous metal foams offer a multitude of advantages over conventional powders as supports for nanostructured heterogeneous catalysts; most critically a preformed 3-D porous framework ensuring full directional coverage of supported catalyst, and intrinsic ease of handling and recyclability. Nonetheless, metal foams remain comparatively underused in thermal catalysis compared to more conventional supports such as amorphous carbon, metal oxides, zeolites and more recently MOFs. Herein, we demonstrate a facile preparation of highly-reactive, robust, and easy to handle Ni foam-supported Cu-based metal catalysts. The highly sustainable synthesis requires no specialized equipment, no surfactants or additive redox reagents, uses water as solvent, and CuCl 2 (H 2 O) 2 as precursor. The resulting material seeds as well-separated micro-crystalline Cu 2 (OH) 3 Cl evenly covering the Ni foam. Calcination above 400 °C transforms the Cu 2 (OH) 3 Cl to highly porous CuO. All materials display promising activity towards the reduction of 4-nitrophenol and methyl orange. Notably, our leading CuO-based material displays 4-nitrophenol reduction activity comparable with very reactive precious-metal based systems. Furthermore, recyclability studies highlight the intrinsic ease of handling for the Ni foam support, and our results point to a very robust, highly recyclable catalyst system.
Direct metal–carbon bonding in symmetric bis(C–H) agostic nickel( i ) complexes
Symmetric Ni( i ) agostic complexes reveal an unusual mode of bonding that is dominated by direct carbon-to-metal charge transfer.