Oxygen Evolution Activity of Amorphous Cobalt Oxyhydroxides: Interconnecting Precatalyst Reconstruction, Long‐Range Order, Buffer‐Binding, Morphology, Mass Transport, and Operation Temperature

Nanocrystalline or amorphous cobalt oxyhydroxides (CoCat) are promising electrocatalysts for the oxygen evolution reaction (OER). While having the same short‐range order, CoCat phases possess different electrocatalytic properties. This phenomenon is not conclusively understood, as multiple interdependent parameters affect the OER activity simultaneously. Herein, a layered cobalt borophosphate precatalyst, Co(H2O)2[B2P2O8(OH)2]·H2O, is fully reconstructed into two different CoCat phases. In contrast to previous reports, this reconstruction is not initiated at the surface but at the electrode substrate to catalyst interface. Ex situ and in situ investigations of the two borophosphate derived CoCats, as well as the prominent CoPi and CoBi identify differences in the Tafel slope/range, buffer binding and content, long‐range order, number of accessible edge sites, redox activity, and morphology. Considering and interconnecting these aspects together with proton mass‐transport limitations, a comprehensive picture is provided explaining the different OER activities. The most decisive factors are the buffers used for reconstruction, the number of edge sites that are not inhibited by irreversibly bonded buffers, and the morphology. With this acquired knowledge, an optimized OER system is realized operating in near‐neutral potassium borate medium at 1.62 ± 0.03 VRHE yielding 250 mA cm−2 at 65 °C for 1 month without degrading performance

Nanostructured Intermetallic Nickel Silicide (Pre)Catalyst for Anodic Oxygen Evolution Reaction and Selective Dehydrogenation of Primary Amines

The development of novel earth-abundant metal-based catalysts to accelerate the sluggish oxygen evolution reaction (OER) is crucial for the process of large-scale production of green hydrogen. To solve this bottleneck, herein, a simple one-pot colloidal approach is reported to yield crystalline intermetallic nickel silicide (Ni2Si), which results in a promising precatalyst for anodic OER. Subsequently, an anodic-coupled electrosynthesis for the selective oxidation of organic amines (as sacrificial proton donating agents) to value-added organocyanides is established to boost the cathodic reaction. A partial transformation of the Ni2Si intermetallic precatalyst generates a porous nickel(oxy)hydroxide phase modified with oxidic silicon species as unequivocally demonstrated by a combination of quasi in situ Raman and X-ray absorption spectroscopy as well as ex situ methods. The activated form of the catalyst generates a geometric current density of 100 mA cm−2 at an overpotential (η100) of 348 mV displaying long-term durability over a week and high efficiency in paired electrolysis

From a Molecular Single-Source Precursor to a Selective High- Performance RhMnOx Catalyst for the Conversion of Syngas to Ethanol

The first carbonyl RhMn cluster Na2[Rh3Mn3(CO)18] 2 has been synthesized and structurally characterized, resulting from the salt metathesis reaction of RhCl3 with Na[Mn(CO)5] 1 in 49% isolated yield. The dianionic Rh3Mn3 cluster core of 2 can serve as a molecular single‐source precursor (SSP) for the low temperature preparation of selective high‐performance RhMn catalysts for the conversion of syngas to ethanol (StE). Impregnation of 2 on silica (davisil) led to three different silica‐supported RhMnOx catalysts with dispersed Rh nanoparticles tightly surrounded by a MnOx matrix. With ethanol selectivities of up to 24.1%, the Rh3Mn3 cluster precursor‐derived catalysts show the highest reported selectivity and performance in the conversion of StE for silica‐supported RhMnOx catalysts

Intermetallic Fe6Ge5Fe_{6} Ge_{5} formation and decay of a core–shell structure during the oxygen evolution reaction

Herein, we report on intermetallic iron germanide ($Fe_{6} Ge_{5}$) as a novel oxygen evolution reaction (OER) precatalyst with a Tafel slope of 32 mV $dec^{−1}$ and an overpotential of 272 mV at 100 mA $cm^{−2}$ in alkaline media. Furthermore, we uncover the in situ formation of a core–shell like structure that slowly collapses under OER conditions

Spectroscopic Characterization, Computational Investigation, and Comparisons of ECX

Three newly synthesized [Na+(221-Kryptofix)] salts containing AsCO–, PCO–, and PCS– anions were successfully electrosprayed into a vacuum, and these three ECX– anions were investigated by negative ion photoelectron spectroscopy (NIPES) along with high-resolution photoelectron imaging spectroscopy. For each ECX– anion, a well-resolved NIPE spectrum was obtained, in which every major peak is split into a doublet. The splittings are attributed to spin–orbit coupling (SOC) in the ECX• radicals. Vibrational progressions in the NIPE spectra of ECX– were assigned to the symmetric and the antisymmetric stretching modes in ECX• radicals. The electron affinities (EAs) and SO splittings of ECX• are determined from the NIPE spectra to be AsCO•: EA = 2.414 ± 0.002 eV, SO splitting = 988 cm–1; PCO•: EA = 2.670 ± 0.005 eV, SO splitting = 175 cm–1; PCS•: EA = 2.850 ± 0.005 eV, SO splitting = 300 cm–1. Calculations using the B3LYP, CASPT2, and CCSD(T) methods all predict linear geometries for both the anions and the neutral radicals. The calculated EAs and SO splittings for ECX• are in excellent agreement with the experimentally measured values. The simulated NIPE spectra, which are based on the calculated Franck–Condon factors, and the SO splittings nicely reproduce all of the observed spectral peaks, thus allowing unambiguous spectral assignments. The finding that PCS• has the greatest EA of the three triatomic molecules considered here is counterintuitive based upon simple electronegativity considerations, but this finding is understandable in terms of the movement of electron density from phosphorus in the HOMO of PCO– to sulfur in the HOMO of PCS–. Comparisons of the EAs of PCO• and PCS• with the previously measured EA values for NCO• and NCS• are made and discussed.National Science Foundation (U.S.) (Grant CHE-1362118

Intermetallic Cobalt Indium Nanoparticles as Oxygen Evolution Reaction Precatalyst: A Non-Leaching p-Block Element

Merely all transition-metal-based materials reconstruct into similar oxyhydroxides during the electrocatalytic oxygen evolution reaction (OER), severely limiting the options for a tailored OER catalyst design. In such reconstructions, initial constituent p-block elements take a sacrificial role and leach into the electrolyte as oxyanions, thereby losing the ability to tune the catalyst's properties systematically. From a thermodynamic point of view, indium is expected to behave differently and should remain in the solid phase under alkaline OER conditions. However, the structural behavior of transition metal indium phases during the OER remains unexplored. Herein, are synthesized intermetallic cobalt indium (CoIn3) nanoparticles and revealed by in situ X-ray absorption spectroscopy and scanning transmission microscopy that they undergo phase segregation to cobalt oxyhydroxide and indium hydroxide. The obtained cobalt oxyhydroxide outperforms a metallic-cobalt-derived one due to more accessible active sites. The observed phase segregation shows that indium behaves distinctively differently from most p-block elements and remains at the electrode surface, where it can form lasting interfaces with the active metal oxo phases

Enabling Iron‐Based Highly Effective Electrochemical Water‐Splitting and Selective Oxygenation of Organic Substrates through In Situ Surface Modification of Intermetallic Iron Stannide Precatalyst

A strategy to overcome the unsatisfying catalytic performance and the durability of monometallic iron‐based materials for the electrochemical oxygen evolution reaction (OER) is provided by heterobimetallic iron–metal systems. Monometallic Fe catalysts show limited performance mostly due to poor conductivity and stability. Here, by taking advantage of the structurally ordered and highly conducting FeSn2 nanostructure, for the first time, an intermetallic iron material is employed as an efficient anode for the alkaline OER, overall water‐splitting, and also for selective oxygenation of organic substrates. The electrophoretically deposited FeSn2 on nickel foam (NF) and fluorine‐doped tin oxide (FTO) electrodes displays remarkable OER activity and durability with substantially low overpotentials of 197 and 273 mV at 10 mA cm−2, respectively, which outperform most of the benchmarking NiFe‐based catalysts. The resulting superior activity is attributed to the in situ generation of α‐FeO(OH)@FeSn2 where α‐FeO(OH) acts as the active site while FeSn2 remains the conductive core. When the FeSn2 anode is coupled with a Pt cathode for overall alkaline water‐splitting, a reduced cell potential (1.53 V) is attained outperforming that of noble metal‐based catalysts. FeSn2 is further applied as an anode to produce value‐added products through selective oxygenation reactions of organic substrates.DFG, 390540038, EXC 2008: Unifying Systems in Catalysis "UniSysCat"TU Berlin, Open-Access-Mittel – 202

Valence isomerization of 2-phospha-4-silabicyclo[1.1.0]butane: a high-level ab initio study

The rearrangements for 2-phospha-4-silabicyclo[1.1.0]butane, analogous to the valence isomerization of the hydrocarbons bicyclobutane, 1,3-butadiene, and cyclobutene, were studied at the (U)QCISD(T)/6-311+G**//(U)QCISD/6-31G* level of theory. The monocyclic 1,2-dihydro-1,2-phosphasiletes are shown to be the thermodynamically preferred product, in contrast to the isomerization of the hydrocarbons, which favors the 1,3-butadiene structure. Furthermore, an unprecedented direct isomerization pathway to the 1,2-dihydro-1,2-phosphasiletes was identified. This pathway is competitive with the isomerization via the open-chain butadienes and becomes favorable when electron-donating substituents are present on silicon

Screening of Heterogeneous Photocatalysts for Water Splitting

In this contribution, a simple method for the screening of photocatalytic activity of catalyst materials is presented. The method is based on two steps the immobilization of the photocatalyst and the subsequent testing of their photocatalytic activity, using the gas evolution at the solid liquid interface. Up to four catalysts can be tested under the same conditions. The observed gas evolution for selected photocatalysts is consistent with trends reported in the literature from conventional photocatalytic reactor