Metal borides have long-standing uses due to their desirable chemical and physical properties such as high melting points, hardness, electrical conductivity, and chemical stability. Typical metal boride preparations utilize high-energy and/or slow thermal heating processes. This report details a facile, solvent-free single-step synthesis of several crystalline metal monoborides containing earth-abundant transition metals. Rapid and exothermic self-propagating solid-state metathesis (SSM) reactions between metal halides and MgB 2 form crystalline FeB, CoB, and NiB in seconds without sustained external heating and with high isolated product yields (∼80%). The metal borides are formed using a well-studied MgB 2 precursor and compared to reactions using separate Mg and B reactants, which also produce self-propagating reactions and form crystalline metal borides. These SSM reactions are sufficiently exothermic to theoretically raise reaction temperatures to the boiling point of the MgCl 2 byproduct (1412 °C). The chemically robust monoborides were examined for their ability to perform electrocatalytic water oxidation and reduction. Crystalline CoB and NiB embedded on carbon wax electrodes exhibit moderate and stable bifunctional electrocatalytic water splitting activity, while FeB only shows appreciable hydrogen evolution activity. Analysis of catalyst particles after extended electrocatalytic experiments shows that the bulk crystalline metal borides remain intact during electrochemical water-splitting reactions though surface oxygen species may impact electrocatalytic activity.

The reactivity of copper oxide (CuO) particles in chemical looping combustion (CLC), a promising indirect combustion process that facilitates carbon capture, was investigated by measuring CuO phase transformations during reduction with methane. By comparing CuO reactivity to iron (α-Fe 2 O 3 ) and cobalt (Co 3 O 4 ) oxides using a continuous flow through system and complementary thermogravimetric analysis, we reveal a link between the solid-state reduction mechanism of CLC oxygen carriers and their size-dependent reactivity toward methane. Reactivity of CuO and Co 3 O 4 is independent of the particle size, with reduction following the nucleation and nuclei growth (NNG) model, whereas α-Fe 2 O 3 shows increased reactivity with decreasing particle size and reduction follows the unreacted shrinking core (USC) model. Supported by density functional theory (DFT) calculations comparing relative energies of formation for surface and bulk oxygen defects, we propose a conceptual framework for the size-dependence of metal oxide oxygen carriers for CLC. For oxygen carriers that reduce via the NNG model, where reduction initiates within the particle core, there will be no size dependence. For reduction via the USC model, where reduction initiates on the particle surface, reactivity will increase for smaller particles. These findings can guide development of metal oxide oxygen carriers for CLC by establishing trends in size-dependent behavior.

We report several new benzoxazaboroles using 2‐aminophenol or 2‐(alkylamino)phenols and phenylboronic acid derivatives. Bis(benzoxazaborole)s were also synthesized using aminophenols and diboronic acids. Characterization of benzoxazaboroles and bis(benzoxazaborole)s was carried out using 1H NMR, 13C NMR, UV–visible, and fluorescence spectroscopic methods along with mass spectrometry and X‐ray crystallography for structural identification. Computational calculations of benzoxazaboroles and bis(benzoxazaborole)s were utilized to support and add to the experimental results. This includes calculations of conformational energies, bond lengths, HOMO‐LUMO energies, and electrostatic potential maps.

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