Replacement of Pt-based oxygen reduction reaction (ORR) catalysts with non-precious metal catalysts (NPMCs) such as Fe/N/C is one of the most important issues in the commercialization of proton exchange membrane fuel cells (PEMFCs). Despite numerous studies on Fe/N/C catalysts, a fundamental study on the development of a versatile strategy is still required for tuning the kinetic activity of a single Fe-N4 site. Herein, we report a new and intuitive design strategy for tuning and enhancing the kinetic activity of a single Fe-N4 site by controlling electron-withdrawing/donating properties of a carbon plane with the incorporation of sulfur functionalities. The effect of electron-withdrawing/donating functionalities was elucidated by experimentation and theoretical calculations. Finally, the introduction of an oxidized sulfur functionality decreases the d-band center of iron by withdrawing electrons, thereby facilitating ORR at the Fe-N4 site by lowering the intermediate adsorption energy. Furthermore, this strategy can enhance ORR activity without a decrease in the stability of the catalyst. This simple and straightforward approach can be a cornerstone to develop optimum NPMCs for application in the cathodes of PEMFCs.

Single-atom catalysts (SACs) have attracted growing attention because they maximizet he number of active sites, with unpredictable catalytic activity.Despite numerous studies on SACs,t here is little researcho nt he support, which is essential to understanding SAC. Herein, we systematically investigated the influence of the support on the performance of the SACb yc omparing with single-atom Pt supported on carbon (Pt SA/C) and Pt nanoparticles supported on WO 3Àx (Pt NP/WO 3Àx ). The results revealed that the support effect was maximized for atomically dispersed Pt supported on WO 3Àx (Pt SA/WO 3Àx ). The Pt SA/WO 3Àx exhibited ahigher degree of hydrogen spillover from Pt atoms to WO 3Àx at the interface, compared with Pt NP/WO 3Àx ,w hichd rastically enhanced Pt mass activity for hydrogen evolution (up to 10 times). This strategy provides an ew framework for enhancing catalytic activity for HER, by reducing noble metal usage in the field of SACs.Hydrogen is being pursued as af uture alternative to fossil fuels and an ideal energy carrier for renewable energy, because it has the highest energy density per mass without any pollutants.Currently,hydrogen production is primarily based on the steam reforming of fossil fuels,w hich is accompanied by environmental issues,s uch as as ubstantial increase in atmospheric CO 2 .Accordingly,itisnecessary to find sustainable and clean alternatives. [1] Electrochemical water splitting is considered ap otentially cost-effective and promising approach for clean hydrogen production. [2] Fort he cathodic hydrogen evolution reaction (HER), platinum (Pt)-based materials are known to the most active electrocatalysts,b ut the high cost and scarcity of Pt are key obstacles to commercial applications of water electrolyzers. [3] Hitherto,n umerous design strategies have been developed for nanostructured electrocatalysts to obtain outstanding electrochemical performance. [4] These strategies are shown to improve the utilization of Pt, and thereby to reduce the use of Pt. Fore xamples,c ore-shell [5] and hollow structures [6] can significantly improve Pt utilization by diminishing the buried non-active Pt atoms inside the particles. From this point of view,single-atom catalysts (SACs), where all metal species are individually dispersed on ad esired support, could be the best candidates to meet this goal, because they offer the maximum number of surface exposed Pt atoms.S everal studies have also demonstrated that Pt SACs show greatly boosted Pt mass activity compared to commercial Pt/C.However,research that considers the effect of the support on SACs performance for the HER is rarely found. [3,7] Thec hoice of support material is one of the most promising strategies for improving (electro)catalysis because interactions between the metal and support can drastically tune the electronic structure of the supported metal, and enhance performance. [8] Furthermore,i th as been recently reported that HER performance can be improved by not only changing the electronic structure of the supported m...

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Herein, a structural design principle is presented to synthesize amorphous bimetallic phosphides (a-CoMoP x /CF) to efficiently catalyze water splitting. Porous Co-MOF/CF and defective CoMoO 4 /CF are used as structureinducing templates to introduce rich defects and large voids that facilitate the formation of amorphous a-CoMoP x /CF. Theoretical calculations reveal a synergistic catalytic mechanism that is based on the bimetallic components. Hierarchical nanosheet arrays combined with amorphous structures provide a superior mass transfer capacity and fully exposed atoms, increasing the electrochemical active surface area (ECSA). The structural advantages and the synergistic catalytic effect of the bimetallic components generate a-CoMoP x / CF with excellent catalytic activity for the hydrogen evolution reaction (HER), displaying a very low overpotential of 59 mV and delivering a current density of 10 mA cm-2 under alkaline conditions. A full electrolysis apparatus with a-CoMoP x /CF as both cathode and anode shows a catalytic performance comparable to that of a noble metal-based catalyst setup (Pt/C-CF // RuO 2-CF), achieving 10 mA cm-2 at a potential of 1.581 V and stable operation at 100 mA cm-2 for more than 100 h. These findings provide a novel concept to design stable structured catalysts based on earth-abundant elements for the large-scale application of electrocatalysis processes related to energy conversion technologies.

A general method to synthesize mesoporous metal oxide@N-doped macroporous graphene composite by heat-treatment of electrostatically co-assembled amine-functionalized mesoporous silica/metal oxide composite and graphene oxide, and subsequent silica removal to produce mesoporous metal oxide and N-doped macroporous graphene simultaneously is reported. Four mesoporous metal oxides (WO 3−x , Co 3 O 4 , Mn 2 O 3 , and Fe 3 O 4 ) are encapsulated in N-doped macroporous graphene. Used as an anode material for sodium-ion hybrid supercapacitors (Na-HSCs), mesoporous reduced tungsten oxide@N-doped macroporous graphene (m-WO 3−x @NM-rGO) gives outstanding rate capability and stable cycle life. Ex situ analyses suggest that the electrochemical reaction mechanism of m-WO 3−x @NM-rGO is based on Na + intercalation/de-intercalation. To the best of knowledge, this is the first report on Na + intercalation/de-intercalation properties of WO 3−x and its application to Na-HSCs.

To overcome inherent limitations of molybdenum carbide (Mo x C) for hydrogen evolution reaction (HER), i.e., low density of active site and nonideal hydrogen binding strength, we report the synthesis of valence-controlled mesoporous Mo x C as a highly efficient HER electrocatalyst. The synthesis procedure uses an interaction mediator (IM), which significantly increases the density of active site by mediating interaction between PEO-b-PS template and Mo source. The valence state of Mo is tuned by systematic control of the environment around Mo by controlled heat treatment under air before thermal treatment at 1100 °C. Theoretical calculations reveal that the hydrogen binding is strongly influenced by Mo valence. Consequently, Mo x C achieves a significant increase in HER activity (exceeding that of Pt/C at high current density ∼35 mA/cm2 in alkaline solution). In addition, a volcano-type correlation between HER activity and Mo valence is identified with various experimental indicators. The present strategies can be applied to various carbide and Mo-based catalysts, and the established Mo valence and HER relations can guide development of highly active HER electrocatalysts.

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Single‐atom catalysts (SACs) have attracted growing attention because they maximize the number of active sites, with unpredictable catalytic activity. Despite numerous studies on SACs, there is little research on the support, which is essential to understanding SAC. Herein, we systematically investigated the influence of the support on the performance of the SAC by comparing with single‐atom Pt supported on carbon (Pt SA/C) and Pt nanoparticles supported on WO3−x (Pt NP/WO3−x). The results revealed that the support effect was maximized for atomically dispersed Pt supported on WO3−x (Pt SA/WO3−x). The Pt SA/WO3−x exhibited a higher degree of hydrogen spillover from Pt atoms to WO3−x at the interface, compared with Pt NP/WO3−x, which drastically enhanced Pt mass activity for hydrogen evolution (up to 10 times). This strategy provides a new framework for enhancing catalytic activity for HER, by reducing noble metal usage in the field of SACs.