Characterization of NiB amorphous alloys with x-ray photoelectron and secondary ion mass spectroscopy

Applications, prospects and challenges of metal borides in lithium sulfur batteries

Although the lithium-sulfur (Li-S) battery has a theoretical capacity of up to 1675 mA h g-1, its practical application is limited owing to some problems, such as the shuttle effect of soluble lithium polysulfides (LiPSs) and the growth of Li dendrites. It has been verified that some transition metal compounds exhibit strong polarity, good chemical adsorption and high electrocatalytic activities, which are beneficial for the rapid conversion of intermediate product in order to effectively inhibit the "shuttle effect". Remarkably, being different from other metal compounds, it is a significant characteristic that both metal and boron atoms of transition metal borides (TMBs) can bind to LiPSs, which have shown great potential in recent years. Here, for the first time, almost all existing studies on TMBs employed in Li-S cells are comprehensively summarized. We firstly clarify special structures and electronic features of metal borides to show their great potential, and then existing strategies to improve the electrochemical properties of TMBs are summarized and discussed in the focus sections, such as carbon-matrix construction, morphology control, heteroatomic doping, heterostructure formation, phase engineering, preparation techniques. Finally, the remaining challenges and perspectives are proposed to point out a direction for realizing high-energy and long-life Li-S batteries.

Ni-Co-B nanoparticle decorated carbon felt by electroless plating as a bi-functional catalyst for urea electrolysis

A free-standing catalyst electrode for urea electrolysis was synthesized by electroless plating of NiCoB alloy onto a flexible carbon felt. The synthesized NiCoB@C catalyst exhibited porous and partially amorphous metallic structure depending on its composition, as analysed by XRD, XPS, and TEM; thus, NiCoB@C catalyst showed a high catalytic activity for urea oxidation reaction as well as hydrogen evolution reaction. The required cell voltage in the electrolysis cell with NiCoB@C as anode and cathode was as low as 1.34 V for the current densities 10 mA cm^-2. Similar performance of the urea electrolysis for H₂ production using 0.33 M urea and a fresh urine in 1 M KOH was observed. The result indicated that NiCoB could be incorporated on to carbon felt by electroless plating, and it could be used as free-standing bifunctional electrodes for urea electrolysis using urea as well as urine.

Measuring and relating the electronic structures of nonmodel supported catalytic materials to their performance

Identifying structure-performance relationships is critical for the discovery and optimization of heterogeneous catalysts. Recent theoretical contributions have led to the development of d-band theory, which relates the calculated electronic structure of a metal to its chemical and catalytic activity. While there are many contributions where quantum-chemical calculations have been utilized to validate the d-band theory, experimental examples relating the electronic structures of commercially relevant nonmodel catalysts to their performance are lacking. We show that even small changes in the near-Fermi-level electronic structures of nonmodel supported catalysts, induced by the formation of surface alloys, can be measured and related to the chemical and catalytic performance of these materials. We demonstrate that critical shifts in the d-band center in alloys are related to the formation of new electronic states in response to alloying rather than to charge redistribution among constitutive alloy elements, i.e., the number of d holes and d electrons localized on the constitutive alloy elements is constant. On the basis of the presented results, we provide a simple, physically transparent framework for predicting shifts in the d-band center in response to alloying and relating these shifts to the chemical characteristics of the alloys.