To reduce the overpotential of electrocatalytic oxygen evolution reaction (OER) for high-efficiency water splitting, a series of 2 to 5 nm ultrafine spinel Co3O4 nanoparticles (NPs) with varied amount of lattice-doped Te (XTe-Co3O4, X represents the nominal molar ratio Te/Co of 0, 2, 4, 6, 8%) as catalysts were prepared through a simple hydrothermal synthesis method. The 6%Te-Co3O4 catalyst was optimized to obtain the overpotential as low as 313 mV at 10 mA cm−2, a small Tafel slope of 75 mV dec−1 in 1 M KOH for OER, outperforming this series and many reported Co3O4-based catalysts. Te doping introduced lattice distortion and resulted in smaller size of Te-Co3O4 NPs with enlarged surface area for more accessible active sites. Oxygen vacancies were created to modify the electronic structure, improve the active sites density, and decrease the kinetic energy barriers of XTe-Co3O4. The electronic conductivity of 6%Te-Co3O4 was improved to accelerate the charge transfer efficiency. All these effects contributed to promoting the reaction kinetics and minimizing the OER overpotentials for high-performance electrocatalysis.
Molybdenum sulfide (MoS2) is considered as low-cost catalyst with great potential for hydrogen evolution reaction (HER). In this contribution, a promising Mo-precursor was first designed and prepared via partial reduction of commercial (NH4)6Mo7O24·4H2O by dl-tartaric acid. A simple pyrolysis method as a new "bottom-up" approach was then developed to achieve the desired HER catalysts by using the Mo-precursor. The resulting catalysts consist of multiphasic 1T/2H-MoS2 and residual S, N co-doped carbon (SNC) with oxygen functional groups. In comparison with (NH4)6Mo7O24·4H2O, Mo-precursor with high content of Mo5+ promotes the full formation of MoS2, while its high content of carbon is more favorable to gain the residual SNC in the resulting catalysts. The further results demonstrate that the percentages of 1T-MoS2 and the content of the residual SNC can be facilely tuned by the pyrolysis temperatures or the Mo/S feeding molar ratios. Notably, although the resulting catalysts exhibit the "bulk" and irregular morphology with low specific surface areas, the high percentages of 1T-MoS2 as the primary advantage, the highly exposed active sites mainly stemming from disordered stacking of S–Mo–S layers, and the high content of the SNC residues are synergistically responsible for their high electrocatalytic HER activity. The high thermal stability of 1T-MoS2 and the excellent durability and stability during HER processes are attributed to the stabilizing effects of the residual SNC. Under the optimized synthetic conditions, the achieved Mo/S(0.2)-450 has a low overpotential of ∼130 mV at 10 mA cm–2, a low Tafel slope of 77 mV dec–1, a high specific activity of 17.53 μA cmCat.–2, and the excellent durability and stability in 0.5 M H2SO4. This work can provide a promising Mo-precursor and a facile route to developing the highly efficient HER catalysts.
Abstract A series of Pd/SBA‐15/Al 2 O 3 /FeCrAl and Pd/5 wt % Ce 1− x Zr x O 2 /SBA‐15/Al 2 O 3 /FeCrAl ( x =0–1) metal monolithic catalysts were prepared and characterized by various techniques. The catalytic activity and the stability of the catalysts for methane combustion were evaluated. All the catalysts retain the SBA‐15 mesoporous structure, with PdO being confined in its channels. The results show that the addition of Ce 1− x Zr x O 2 as promoters can improve the activity and stability of the catalysts. The stabilities of the metal monolithic catalysts are much better than those of Pd/SBA‐15 particle catalysts. The catalyst with ZrO 2 as promoter exhibits the best activity and stability (T 90 =395 °C ) , and the conversion of methane remains constant during the 700 h test.
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