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Electrocatalytic water splitting (EWS) is a promising route to produce hydrogen in a sustainable and environment-benign manner. To realize the large-scale hydrogen production, it is paramount to develop desirable electrocatalysts with engineered structure, high catalytic activity, facile accessibility, low cost, and good durability. Of late, boride-based materials, especially transition-metal borides (TMBs), are emerging as promising candidates for the EWS process. However, so far, little attempt has been made to provide a comprehensive summary on these findings. Herein, this review provides the up-to-date status on upgrading the catalytic performance of TMB-based nanomaterials by regulating the internal and external characteristics. The conventional synthetic techniques are first presented for the preparation of TMB-based catalysts. Afterwards, the advanced strategies are summarized to enhance the catalytic performance of TMBs, including morphology control, component regulation, phase engineering, surface oxidation and hybridization. Then, the design principles of TMB-based electrocatalysts for high-performance EWS are outlined. Lastly, the current challenges and future directions in the development of TMB-based materials are proposed. This review article is expected to envisage insights into the TMBs-based water splitting and to provide strategies for design of the next-generation TMB-based electrocatalysts.

The oxidation resistance of Hf B and Hf Al B thin films was investigated comparatively at 700 °C for up to 8 h. Single-phase solid solution thin films were co-sputtered from HfB and AlB compound targets. After oxidation at 700 °C for 8 h an oxide scale thickness of 31   2 nm was formed on Hf Al B which corresponds to 14% of the scale thickness measured on Hf B . The improved oxidation resistance can be rationalized based on the chemical composition and the morphology of the formed oxide scales. On Hf B the formation of a porous, O, Hf, and B-containing scale and the formation of crystalline HfO is observed. Whereas on Hf Al B a dense, primarily amorphous scale containing O, Al, B as well as approximately 3 at% of Hf forms, which reduces the oxidation kinetics significantly by passivation. Benchmarking Hf Al B with Ti-Al-based boride and nitride thin films with similar Al concentrations reveals superior oxidation behavior of the Hf-Al-based thin film. The incorporation of few at% of Hf in the oxide scale decelerates oxidation kinetics at 700 °C and leads to a reduction in oxide scale thickness of 21% and 47% compared to Ti Al B and Ti Al N , respectively. Contrary to Ti-Al-based diborides, Hf Al B shows excellent oxidation behavior despite B-richness.

While boron forms a wide range of metal borides with important industrial applications, there has been relatively little attention devoted to lanthanide boride clusters. Here we report a joint photoelectron spectroscopy and quantum chemical study on two octa-boron di-lanthanide clusters, Ln₂B₈⁻ (Ln = La, Pr). We found that these clusters form highly stable inverse sandwich structures, [Ln–B₈–Ln]⁻, with strong Ln and B₈ bonding via interactions between the Ln 5d orbitals and the delocalized σ and π orbitals on the B₈ ring. A (d–p)δ bond, involving the 5dδ and the antibonding π orbital of the B₈ ring, is observed to be important in the Ln–B₈ interactions. The highly symmetric inverse sandwich structures are overwhelmingly more stable than any other isomers. Upon electron detachment, the (d–p)δ orbitals become half-filled, giving rise to a triplet ground state for neutral La₂B₈. In addition to the two unpaired electrons in the (d–p)δ orbitals upon electron detachment, the neutral Pr₂B₈ complex also contains two unpaired 4f electrons on each Pr center. The six unpaired spins in Pr₂B₈ are ferromagnetically coupled to give rise to a septuplet ground state. The current work suggests that highly magnetic Ln…B₈…Ln inverse sandwiches or 1D Ln…B₈…Ln nanowires may be designed with novel electronic and magnetic properties.

Urea is an important raw material in the chemical industry and is widely used as a nitrogen source in chemical fertilizers. The current industrial urea synthesis not only requires harsh reaction conditions, but also consumes most of the NH 3 obtained through artificial synthesis. The conversion of N 2 and CO 2 into urea through electrochemical reactions under ambient conditions represents a novel green urea synthesis method. However, the large-scale promotion of this method is limited by the lack of suitable electrocatalysts. Here, by means of density functional theory computations, we systematically study the catalytic activity of three experimentally available two-dimensional metal borides (MBenes), Mo 2 B 2 , Ti 2 B 2 , and Cr 2 B 2 toward simultaneous electrocatalytic coupling of N 2 and CO 2 to produce urea under ambient conditions. According to our results, these three MBenes not only have superior intrinsic basal activity for urea formation, with limiting potentials ranging from −0.49 to −0.65 eV, but also can significantly suppress the competitive reaction of N 2 reduction to NH 3 . In particular, 2D Mo 2 B 2 and Cr 2 B 2 possess superior capacity to suppress surface oxidation and self-corrosion under electrochemical reaction conditions, rendering them relatively promising electrocatalysts for urea production. Our work paves the way for the electrochemical synthesis of urea. The conversion of N 2 and CO 2 into urea through electrochemical reactions under ambient conditions represents a novel green urea synthesis method. Here, the authors demonstrate that two-dimensional transition metal borides can serve as effective catalysts for electrochemical urea synthesis.

The need for improved functionalities in extreme environments is fuelling interest in high-entropy ceramics 1 – 3 . Except for the computational discovery of high-entropy carbides, performed with the entropy-forming-ability descriptor 4 , most innovation has been slowly driven by experimental means 1 – 3 . Hence, advancement in the field needs more theoretical contributions. Here we introduce disordered enthalpy–entropy descriptor (DEED), a descriptor that captures the balance between entropy gains and enthalpy costs, allowing the correct classification of functional synthesizability of multicomponent ceramics, regardless of chemistry and structure. To make our calculations possible, we have developed a convolutional algorithm that drastically reduces computational resources. Moreover, DEED guides the experimental discovery of new single-phase high-entropy carbonitrides and borides. This work, integrated into the AFLOW computational ecosystem, provides an array of potential new candidates, ripe for experimental discoveries. DEED captures the balance between entropy gains and costs, allowing the correct classification of functional synthesizability of multicomponent ceramics, regardless of chemistry and structure, and provides an array of potential new candidates, ripe for experimental discoveries.

Ultra-high temperature ceramics (UHTCs) are generally referred to the carbides, nitrides, and borides of the transition metals, with the Group IVB compounds (Zr & Hf) and TaC as the main focus. The UHTCs are endowed with ultra-high melting points, excellent mechanical properties, and ablation resistance at elevated temperatures. These unique combinations of properties make them promising materials for extremely environmental structural applications in rocket and hypersonic vehicles, particularly nozzles, leading edges, and engine components, etc. In addition to bulk UHTCs, UHTC coatings and fiber reinforced UHTC composites are extensively developed and applied to avoid the intrinsic brittleness and poor thermal shock resistance of bulk ceramics. Recently, highentropy UHTCs are developed rapidly and attract a lot of attention as an emerging direction for ultra-high temperature materials. This review presents the state of the art of processing approaches, microstructure design and properties of UHTCs from bulk materials to composites and coatings, as well as the future directions.

IMPACT STATEMENT Two-dimensional magnetic hexagonal and orthorhombic M3B4 compounds with significant stiffness to preserve their magnetic properties were discovered using DFT calculations and MC simulations.

A new class of high-entropy M 3 B 4 borides of the Ta 3 B 4 -prototyped orthorhombic structure has been synthesized in the bulk form for the first time. Specimens with compositions of (V 0.2 Cr 0.2 Nb 0.2 Mo 0.2 Ta 0.2 ) 3 B 4 and (V 0.2 Cr 0.2 Nb 0.2 Ta 0.2 W 0.2 ) 3 B 4 were fabricated via reactive spark plasma sintering of high-energy-ball-milled elemental boron and metal precursors. The sintered specimens were ∼98.7% in relative densities with virtually no oxide contamination, albeit the presence of minor (4–5 vol%) secondary high-entropy M 5 B 6 phases. Despite that Mo 3 B 4 or W 3 B 4 are not stable phase, 20% of Mo 3 B 4 and W 3 B 4 can be stabilized into the high-entropy M 3 B 4 borides. Vickers hardness was measured to be 18.6 and 19.8 GPa at a standard load of 9.8 N. This work has further expanded the family of different structures of high-entropy ceramics reported to date.

Metal borides/borates have been considered promising as oxygen evolution reaction catalysts; however, to date, there is a dearth of evidence of long-term stability at practical current densities. Here we report a phase composition modulation approach to fabricate effective borides/borates-based catalysts. We find that metal borides in-situ formed metal borates are responsible for their high activity. This knowledge prompts us to synthesize NiFe-Boride, and to use it as a templating precursor to form an active NiFe-Borate catalyst. This boride-derived oxide catalyzes oxygen evolution with an overpotential of 167 mV at 10 mA/cm 2 in 1 M KOH electrolyte and requires a record-low overpotential of 460 mV to maintain water splitting performance for over 400 h at current density of 1 A/cm 2 . We couple the catalyst with CO reduction in an alkaline membrane electrode assembly electrolyser, reporting stable C 2 H 4 electrosynthesis at current density 200 mA/cm 2 for over 80 h. Metal borides/borates are promising candidates to become high-performance alkaline oxygen evolution reaction catalysts. This study reports an in-situ phase composition modulation approach to fabricate boride/borate-based catalysts.

All-in-one radiation shielding is an emerging concept in developing new-generation radiation protection materials since various forms of ionizing radiation, such as neutrons and gamma rays, can occur simultaneously. In this study, we examine the ability of transition metal borides to attenuate both photon and particle radiation. Specifically, fourteen different transition metal borides (including inner transition metal borides) are selected for examination based on their thermodynamic stabilities, molecular weights, and neutron capture cross-sections of the elements they contain. Radiation shielding characteristics of the transition metal borides are computationally investigated using Phy-X/PSD, EpiXS and NGCal software. The gamma-ray shielding capabilities of the transition metal borides are evaluated in terms of the mass attenuation coefficient (μm), the linear attenuation coefficient (µ), the effective atomic number (Zeff), the half-value layer (HVL), the tenth-value layer (TVL), and the mean free path (MFP). The mass and linear attenuation factors are identified for thermal and fast neutrons at energies of 0.025 eV and 4 MeV, respectively. Moreover, the fast neutron removal cross-sections (∑R) of the transition metal borides are calculated to assess their neutron shielding abilities. The results revealed that borides of transition metals with a high atomic number, such as Re, W, and Ta, possess outstanding gamma shielding performance. At 4 MeV photon energy, the half-value layers of ReB2 and WB2 compounds were found as 1.38 cm and 1.43 cm, respectively. Most notably, these HVL values are lower than the HVL value of toxic Pb (1.45 cm at 4 MeV), which is one of the conventional radiation shielding materials. On the other hand, SmB6 and DyB6 demonstrated exceptional neutron attenuation for thermal and fast neutrons due to the high neutron capture cross-sections of Sm, Dy, and B. The outcomes of this study reveal that transition metal borides can be suitable candidates for shielding against mixed neutron and gamma radiation.