Vacancy-rich heterogeneous MnCo2O4.5@NiS electrocatalyst for highly efficient overall water splitting

Alkaline water electrolysis is regarded as a promising technology for sustainable energy conversion. Spinel oxides have attracted considerable attention as potential catalysts because of their diverse metal valence states. However, achieving the required current densities at low voltages is a challenge due to its limited active sites and suboptimal electron transport. In this study, we present a novel bifunctional catalyst composed of MnCo2O4.5 nanoneedles grown on NiS nanosheets for water electrolysis. Remarkably, MnCo2O4.5@NiS demonstrates exceptional catalytic activity, requiring 187 and 288 mV to achieve a current density of 100 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. The impressive performance of MnCo2O4.5@NiS is demonstrated by the lower value of voltage 1.44 V needed to deliver the current density of 10 mA cm-2, which outperformed the 1.66 V required for a commercial Pt/C||RuO2 system. Detailed structure analysis and density functional theory (DFT) calculations reveal that the MnCo2O4.5@NiS heterostructure enhances electron transfer at the interface, promotes the formation of oxygen vacancies and tunes the electronic structures of Mn and Co. These findings underscore the potential of MnCo2O4.5@NiS as an efficient and cost-effective electrocatalyst for hydrogen production.

Construction of MnxCoyO4/Ti electrocatalysts for efficient bifunctional water splitting

In this work, we report the design and synthesis of non-noble metal-based electrocatalysts for effective overall water splitting in alkaline solutions for the development of hydrogen energy. The electrocatalysts were synthesized by a one-step hydrothermal method similar to microflower structure electrocatalysts. The synergistic effect between the special Echinops sphaerocephalus nanostructure and the nanowire can greatly improve the conductivity of the nanomaterial due to its high activity quality, fast ion transport, and exposure of more active sites, thus resulting in a better catalytic activity and a longer material stability of the electrocatalyst. For Mn_xCo_yO₄/Ti in alkaline aqueous solutions, a current density of 10 mA cm^-2 is required when the voltage is only 1.60 V. In addition, the hydrogen evolution activity of electrocatalysts is 168 mV at 10 mA cm^-2, the Tafel slope is 174 mV dec^-1, and the oxygen evolution activity of electrocatalysts is 229 mV at 10 mA cm^-2, which showed good long-term stability within 12 h, even better than that of previously reported electrocatalysts.

Metal-Organic Framework-Derived Hollow CoSx Nanoarray Coupled with NiFe Layered Double Hydroxides as Efficient Bifunctional Electrocatalyst for Overall Water Splitting

For effective hydrogen production by water splitting, it is essential to develop earth-abundant, highly efficient, and durable electrocatalysts. Herein, the authors report a bifunctional electrocatalyst composed of hollow CoS_x and Ni-Fe based layered double hydroxide (NiFe LDH) nanosheets for efficient overall water splitting (OWS). The optimized heterostructure is obtained by the electrodeposition of NiFe LDH nanosheets on metal-organic framework-derived hollow CoS_x nanoarrays, which are supported on nickel foam (H-CoS_x @NiFe LDH/NF). The unique structure of the hybrid material not only provides ample active sites, but also facilitates electrolyte penetration and gas release during the reactions. Additionally, the strong coupling and synergy between the hydrogen evolution reaction (HER) active CoS_x and the oxygen evolution reaction (OER) active NiFe LDH gives rise to the excellent bifunctional properties. Consequently, H-CoS_x @NiFe LDH/NF exhibits remarkable HER and OER activities with overpotentials of 95 and 250 mV, respectively at 10 mA cm^-2 in 1.0 M KOH. Even at 1.0 A cm^-2 , the electrode requires small overpotentials of 375 mV (for HER) and 418 mV (for OER), respectively. An electrolyzer based on H-CoS_x @NiFe LDH/NF demonstrates a low cell voltage of 1.98 V at a current density of 300 mA cm^-2 and good durability for 100 h in OWS application.