Developing the high-performance intermetallic bi–metal boride OER catalysts with a high density of grain boundaries and appropriate electronic structure is still a challenge. Herein, we synthesized an intermetallic (Fe x Co 1− x ) 2 B OER catalyst (GB-(Fe x Co 1− x ) 2 B) with controllable grain boundary densities by a facile ball-milling method. Benefiting from the modulation of both grain boundary density and electronic structure, the GB-(Fe 0.66 Co 0.34 ) 2 B supported on reduced graphene oxide shows a low OER overpotential of 221 mV at a current density of 10 mA cm −2 and Tafel slope of 38.2 mV dec −1 . The experimental and theoretical calculated methods demonstrate that the Fe introduction into the intermetallic Co 2 B catalyst can produce the higher grain boundary density and modulate the electronic structure, respectively. This work provides a promising insight in understanding the synergetic effects in bimetallic for GB-(Fe x Co 1− x ) 2 B systems and supports a new strategy to explore other efficient catalysts with a high density of grain boundaries.
The internal barrier layer capacitance effect substantially contributes to the colossal permittivity in In and Nb co-doped TiO 2 (INTO) ceramics. Therefore, enhancing grain boundary density and ceramic compactness can efficaciously reduce their low-frequency dielectric loss . In this investigation, Bi 2 O 3 addition was utilized to aid sintering and refine grains for INTO ceramics. The results reveal that Bi-doped INTO ceramics, in contrast to their undoped counterparts, exhibit a more refined and compact grain structure with a significant increase in the quantity of grain boundaries. Moreover, a noticeable reduction in low-frequency dielectric loss from above 0.1 to below 0.05 and enhanced frequency stability of permittivity from below 10 Hz to approximately 10 kHz were observed, along with a decrease in the sintering temperature to 1300 °C. In comparison to undoped INTO ceramics, Bi doping also enhances the withstand voltage capability by a factor of 1.5–4 for Bi-doped INTO ceramics. However, as the sintering temperature of Bi-doped INTO ceramics increases and the grain size enlarges, their breakdown voltage gradually decreases, but the non-linear coefficient of current-voltage characteristics progressively increases. Analysis of complex impedance spectra confirms that the increased grain boundary density and resistance in Bi-doped INTO ceramics is the primary factor for the enhanced dielectric properties and withstand voltage capability.
Hu Tian-Jun,Li Yi-Fan,Tian Yu-Zhu,Wang Ying,Chen Ya-Ru,Zhang Jun-Ming,Luo Er-Gui,Jia Jian-Feng
Exploring the structure–activity relationship between the performance of gas sensors and the structure of semiconductor metal oxide (SMO) nanomaterials is crucial for understanding and designing gas-sensing materials and overcoming the application limitations of SMO-based gas sensors. Regulation of a single SMO microstructure provides a promising solution to address this scientific problem due to its controllable composition. In this study, we control the grain boundary (GB) density of Fe 2 O 3 nanomaterials using a simple solvothermal method. They have similar chemical compositions and crystal phases, providing an ideal platform for studying the influence of the GB density on the gas-sensing performance. Gas-sensing tests showed that the Fe 2 O 3 -1 sensor with medium GB density and the Fe 2 O 3 -2 sensor with high GB density had higher sensitivity and selectivity than the Fe 2 O 3 -0 sensors with low GB density before reaching the optimal operating temperature. However, when the GB density increased, the response to acetone decreased slightly, whereas the optimal operating temperature decreased. This work highlights the unique performance of the GB density in enhancing the gas sensitivity of a single SMO. Graphical abstract
Despite the ultrahigh energy density of rechargeable lithium–oxygen (Li-O2) batteries, their practical use is still hindered by the poor performance of electrocatalysts. Recently, porous and hollow nanostructured catalysts have been found to be promising electrocatalysts toward the ORR/OER to improve the performance of Li-O2 batteries. However, the catalytic activities of the catalysts are still insufficient and the nanopores are easily clogged by the insoluble discharge products. Herein, highly porous and hollow TiO2–x nanoboxes (TiO2–x NBs) with large surface areas, increased oxygen vacancies, and high grain boundary density have been developed as an electrocatalyst for Li-O2 batteries via a cation-assisted synthetic approach. The Li-O2 batteries with TiO2–x NBs as the electrocatalyst exhibit a high specific capacity of 8569 mA h g–1, excellent rate capability, and long cycle life up to 200 cycles when the capacity is limited to 1000 mA h g–1. Moreover, this cation-assisted approach for fine-tuning the nanostructure could be an innovative strategy to design efficient electrocatalysts for high-performance Li-O2 batteries.
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