the anode, required the large overpotential (η) to overcome the sluggish kinetically and hindered practical utilization of water splitting technology. [7][8][9] Efficient catalysts should be designed and synthesized to decrease the overpotential and accelerate the kinetically for the OER. Although state-of-the-art precious metalbased materials (e.g., RuO 2 or IrO 2 ) are the benchmark catalysts for OER, they are very costly due to their limited resources on earth. [10,11] Huge efforts have therefore been devoted to fabricate efficient and alternative electrocatalysts.Over the last few decades, extensive attentions have been paid to earth-abundant and cost-efficient (3d) transition metal-based alternatives. [1,7,9,12] Apart from the well-developed metal oxides and (oxy)hydroxides catalysts, [2,13]

This study describes a facile and effective route to synthesize hybrid material consisting of Co3O4 nanoparticles anchored on nitrogen-doped reduced graphene oxide (Co3O4/N-rGO) as a high-performance tri-functional catalyst for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and H2O2 sensing. Electrocatalytic activity of Co3O4/N-rGO to hydrogen peroxide reduction was tested by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry. Under a reduction potential at −0.6 V to H2O2, this constructing H2O2 sensor exhibits a linear response ranging from 0.2 to 17.5 mM with a detection limit to be 0.1 mM. Although Co3O4/rGO or nitrogen-doped reduced graphene oxide (N-rGO) alone has little catalytic activity, the Co3O4/N-rGO exhibits high ORR activity. The Co3O4/N-rGO hybrid demonstrates satisfied catalytic activity with ORR peak potential to be −0.26 V (vs. Ag/AgCl) and the number of electron transfer number is 3.4, but superior stability to Pt/C in alkaline solutions. The same hybrid is also highly active for OER with the onset potential, current density and Tafel slope to be better than Pt/C. The unusual catalytic activity of Co3O4/N-rGO for hydrogen peroxide reduction, ORR and OER may be ascribed to synergetic chemical coupling effects between Co3O4, nitrogen and graphene.

In this work, we report the remarkable catalytic effects of a novel Ti3C2 MXene-based catalyst (Ni@Ti-MX), which was prepared via self-assembling of Ni nanoparticles onto the surface of exfoliated Ti3C2 nanosheets. The resultant Ni@Ti-MX catalyst, characterized by ultradispersed Ni nanoparticles being anchored on the monolayer Ti3C2 flakes, was introduced into MgH2 through ball milling. In situ transmission electron microscopy (TEM) analysis revealed that a synergetic catalytic effect of multiphase components (Mg2Ni, TiO2, metallic Ti, etc.) derived in the MgH2 + Ni@Ti-MX composite exhibits remarkable improvements in the hydrogen sorption kinetics of MgH2. In particular, the MgH2 + Ni@Ti-MX composite can absorb 5.4 wt % H2 in 25 s at 125 °C and release 5.2 wt % H2 in 15 min at 250 °C. Interestingly, it can uptake 4 wt % H2 in 5 h even at room temperature. Furthermore, the dehydrogenation peak temperature of the MgH2 + Ni@Ti-MX composite is about 221 °C, which is 50 and 122 °C lower than that of MgH2 + Ti-MX and MgH2, respectively. The excellent hydrogen sorption properties of the MgH2 + Ni@Ti-MX composite are primarily attributed to the peculiar core–shell nanostructured MgH2@Mg2NiH4 hybrid materials and the interfacial coupling effects from different catalyst–matrix interfaces. The results obtained in this study demonstrate that using self-assembling of transition-metal elements on two-dimensional (2D) materials as a catalyst is a promising approach to enhance the hydrogen storage properties of MgH2.

aMoSx/Co(OH)2 nanosheets were synthesized by forming amorphous MoSx on Co(OH)2 nanosheets. The aMoSx/Co(OH)2 nanosheets demonstrate excellent OER catalytic activity with only 350 mV at 10 mA cm−2. The incorporation of amorphous molybdenum sulfide enhances the hydrophilicity, favoring the availability of reactant, and induces electron transfer for enhancing the OER catalytic activity of Co(OH)2.

No abstract

MXenes are considered as potential support materials for nanoconfinement of MgH2/Mg to improve the hydrogen storage properties. However, it has never been realized so far due to the stacking and oxidation problems caused by unexpected surface terminations (−OH, −O, etc.) on MXenes. In this study, hexadecyl trimethylammonium bromide was used to build a 3D Ti3C2T x architecture of folded nanosheets to reduce the stacking risk of flakes, and a bottom-up self-assembly strategy was successfully applied to synthesize ultradispersed MgH2 nanoparticles anchored on the surface of the annealed 3D Ti3C2T x (Ti-MX). The composite with a 60 wt % loading of MgH2 NPs, 60MgH2@Ti-MX, starts to decompose at 140 °C and is capable of releasing 3.0 wt % H2 at 150 °C within 2.5 h. In addition, a reversible capacity up to 4.0 wt % H2 was still maintained after 60 cycles at 200 °C without obvious loss in kinetics. In situ high-resolution TEM observations of the decomposition process together with other analyses revealed that the nanosize effect caused by the nanoconfinement and the multiphasic interfaces between MgH2(Mg) and Ti-MX, especially the in situ formed catalytic TiH2, were main reasons accounting for the superior hydrogen sorption performances.

No abstract

MgH2 has attracted intensive interests as one of the most promising hydrogen storage materials. Nevertheless, the high desorption temperature, sluggish kinetics, and rapid capacity decay hamper its commercial application. Herein, 2D TiO2 nanosheets with abundant oxygen vacancies are used to fabricate a flower-like MgH2/TiO2 heterostructure with enhanced hydrogen storage performances. Particularly, the onset hydrogen desorption temperature of the MgH2/TiO2 heterostructure is lowered down to 180 °C (295 °C for blank MgH2). The initial desorption rate of MgH2/TiO2 reaches 2.116 wt% min−1 at 300 °C, 35 times of the blank MgH2 under the same conditions. Moreover, the capacity retention is as high as 98.5% after 100 cycles at 300 °C, remarkably higher than those of the previously reported MgH2-TiO2 composites. Both in situ HRTEM observations and ex situ XPS analyses confirm that the synergistic effects from multi-valance of Ti species, accelerated electron transportation caused by oxygen vacancies, formation of catalytic Mg-Ti oxides, and stabilized MgH2 NPs confined by TiO2 nanosheets contribute to the high stability and kinetically accelerated hydrogen storage performances of the composite. The strategy of using 2D substrates with abundant defects to support nano-sized energy storage materials to build heterostructure is therefore promising for the design of high-performance energy materials.