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The exploration of new heterojunction materials is of great significance in reducing the cost of existing noble metal catalysts and thus realizing the large-scale application of electrocatalytic hydrolysis technology. Herein, a novel CoP/CoMoP2 heterojunction was synthesized and served as a hydrogen evolution reaction (HER) electrocatalyst. The heterojunction has morphology of nanoporous structure, which is conducive to exposing more active sites and facilitating bubbles transport. The charge distribution is optimized by a strong interface interaction between CoP and CoMoP2. The catalyst's conductivity and the adsorption properties of the intermediates have both been enhanced. CoP/CoMoP2 demonstrates excellent HER activity with an overpotential of 93.6 mV at 10 mA·cm−2, which is competitive with the reported performance of analogous electrocatalysts. This work provides insights into the development of innovative phosphide-based heterojunction electrocatalysts. [ABSTRACT FROM AUTHOR]

The electrocatalytic hydrogen evolution activity of transition metal sulfide heterojunctions are significantly increased when compared with that of a single component, but the mechanism behind the performance enhancement and the preparation of catalysts with specific morphologies still need to be explored. Here, we prepared a Co9S8/MoS2 heterojunction with microsphere morphology consisting of thin nanosheets using a facile two-step method. There is electron transfer between the Co9S8 and MoS2 of the heterojunction, thus realizing the redistribution of charge. After the formation of the heterojunction, the density of states near the Fermi surface increases, the d-band center of the transition metal moves downward, and the adsorption of both water molecules and hydrogen by the catalyst are optimized. As a result, the overpotential of Co9S8/MoS2 is superior to that of most relevant electrocatalysts reported in the literature. This work provides insight into the synergistic mechanisms of heterojunctions and their morphological regulation. [ABSTRACT FROM AUTHOR]

A high-chromium alloy with 2Cr32Si2MnMo2 available for diesel engine valve seats was fabricated by centrifugal casting to improve valve seat quality. The friction and wear performances of the valve seat dry sliding against an exhaust valve were measured using a SRV testing machine. The test procedures include temperature and load sensitivities and wear. The test temperatures ranged from 100 ℃ to 280 ℃ and loads from 50 to 125 N. The friction and wear of the valve seat were found to decrease first and then increase with the increment of temperature or load. Scanning electron microscopy and energy dispersive X-ray spectroscopy analyses revealed the tribofilms contained more friction-increasing Cr2O3 and the wear mechanism was a complicated combination of two-body abrasion, three-body abrasion and oxidation. The strong adhesion between the valve and its seat arrested the relative sliding, but with loads going up to 150 N. In most cases, the valve had unexpectedly higher wear resistance than that of its seat over the temperature range, which is ascribed to adhesion to the tribofilms. [ABSTRACT FROM PUBLISHER]

Modulating the electronic states of electrocatalysts is critical for achieving efficient hydrogen evolution reaction (HER). However, how to develop electrocatalysts with superior electronic states is an urgent challenge that must be addressed. Herein, we prepared the CoP/MoS 2 heterojunction with a microsphere morphology consisting of thin nanosheets using a facile two-step method. The catalyst's ultrathin nanosheet structure not only provides an extensive surface area for exposing active sites, but it also enables ion transport and bubble release. Electron transfer occurs between CoP and MoS 2 , optimizing the heterojunction's charge distribution and enhancing the intermediates' adsorption capabilities. As a result, the CoP/MoS 2 heterojunction exhibits outstanding electrocatalytic hydrogen evolution activity with an overpotential of only 88 mV at a current density of 10 mA cm -2 , which exceeds both the sulfide heterojunction Co 9 S 8 /MoS 2 and the phosphide heterojunction CoP/CoMoP 2 . The experimental results and DFT calculation results show that the former has stronger synergistic effects and higher HER activity. This work sheds light on the exploration of efficient heterojunction electrocatalysts with excellent electronic structures., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)