Bifunctional Electrocatalysts For Oxygen Evolution Reactions Research Articles

Zinc oxide nanoflakes supported copper oxide nanosheets as a bifunctional electrocatalyst for OER and HER in an alkaline medium

Bifunctional electrocatalysts are the attractive research in the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in the overall water-splitting reactions. The design and development of the cost-effective OER/HER bifunctional electrocatalysts with superior catalytic activity are still remaining as the big challenges. Herein, we have developed the CuO–ZnO nanocomposite as a bifunctional OER/HER electrocatalyst via simple chemical precipitation method. The nanocomposite was investigated for its crystalline structure, surface morphology and the functions of elements using XRD, FT-IR, SEM, TEM and XPS characterization techniques, respectively. The nanocomposite exhibited the excellent activity for the overall water-splitting in an alkaline medium. The CuO–ZnO nanocomposite showed the less onset potential of 1.4 and 0.15 V versus RHE in 1M KOH (Tafel slopes value of 0.180 and 0.400 V dec−1) for OER and HER, respectively. Hence, the as-prepared bifunctional electrocatalyst displayed the high stability for 10 h in the water electrolysis processes.

Copper-cobalt bimetallic conductive metal–organic frameworks as bifunctional oxygen electrocatalyst in alkaline and neutral media

The preparation of low cost bifunctional electrocatalysts that efficiently catalyze oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is a crucial step towards realizing high-performance Zn–air batteries. Herein a bimetallic CuCo-HITP (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) conductive metal-organic frameworks (MOFs) was synthesized as a bifunctional electrocatalyst for OER and ORR through an effective and facile ammonia-assisted method. Structural characterization showed that the metal ions coordinated with HITP ligands through strong coordination bonds of M − N4 to construct a two-dimensional (2D) porous structure. The electrochemical tests demonstrated that CuCo-HITP had superior bifunctional OER and ORR electrocatalytic performance in both alkaline and neutral media. It should be attributed to the bimetallic synergistically effect, which lead to more active sites, faster charge transfer rate and improvement of the catalytic reaction kinetics.

Development of robust noble-metal free lanthanum, neodymium doped Li1.05Ni0.5Mn1.5O4 as a bifunctional electrocatalyst for electrochemical water splitting.

Catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are at the heart of water oxidation reactions. Despite continuous efforts, the development of OER/HER electrocatalysts with high activity at low cost remains a big challenge. Herein, we report a composite material consisting of Li1.05Ni0.5Mn1.5O4, Li1.05Ni0.5 La0.10Mn1.40O4, and Li1.05Ni0.5 Nd0.10Mn1.40O4 as a bifunctional electrocatalyst for OER and HER applications. Though the catalyst has a modest activity for HER, it exhibits high OER activity thereby making it a better nonprecious electrocatalyst for both OER and HER. The catalytic activity arises from the synergetic effects between LNM-La and LNM-Nd by a facile route that shows excellent and durable bifunctional catalytic activity for OER and HER in the alkaline medium developed. The LNM, LNM-La, and, LNM-Nd displayed current densities of 2.17 V, 1.68 V, and 1.93 V vs. RHE at 10 mA cm-2 respectively. The Tafel slope values obtained for LNM, LNM-La, and LNM-Nd are about 419 mV dec-1, 118 mV dec-1, and 378 mV dec-1 respectively. These results indicate the superior electrocatalytic activity of LNM-La with facile OER kinetics.

Unveiling the boosting of metal organic cage leaching substance on the electrocatalytic oxygen evolution reaction

Catalysts often undergo changes during the process of catalytic reactions, which makes the whole catalytic reaction system complicated and brings about much difficulty for the exploration of catalytic mechanism. Herein, we report that an octahedral metal organic cage (MOC) with stress was directionally transformed into two-dimensional nanoarrays maintaining the structure of precursor and new soluble low-nuclear complexes during the electrocatalytic oxygen evolution reaction (OER). The in-situ generated miscible electrocatalyst exhibits an overpotential as low as 197 mV at 10 mA cm−2, with a high electrochemical stability up to 5 h. Notably, the miscible catalyst can be used as bifunctional electrocatalyst for OER and hydrogen evolution reaction (HER) and exhibits an ultra-low overpotential of 293 mV, even achieve overall water splitting under the voltage provided by a 1.5 V AA battery. As revealed by density functional theory simulations, the position of SO42− in MOC heterogeneous catalyst is regulated by the soluble low-nuclear complexes to reduce the activation energy of the reaction, leading to an optimization of the OER activity for the reaction system. This work provides a new strategy for the rational design of high-efficiency electrocatalytic system.

Tuning the morphology and electron structure of metal-organic framework-74 as bifunctional electrocatalyst for OER and HER using bimetallic collaboration strategy

Compared to traditional 3D bulk metal-organic frameworks (MOFs), 2D MOFs are recently considered as an ideal electrocatalyst because they possess several advantages containing nanometer thickness for the efficient mass transport and enlarged surface areas containing more available active metal sites. In this work, the 2D NiFe-MOF-74 nanosheets directly growing on nickel foam (NF) are fabricated by a one-step solvothermal process without using annealing treatment. Remarkably, it is noted that thin layered MOF shape can be obtained by the collaboration of two metals, Ni and Fe which favors in maximum utilization of the active sites. Also, the electron environment of Ni and Fe, together with the conductivity of MOF-74 can be tuned by the cooperative effect of two metals. The optimized NiFe-MOF-74 electrode displays higher activity than that of a metal MOF-74 and the benchmarking catalysts for oxygen evolution reaction (OER), which drives a current density of 10 mA cm−2 at the overpotentials of only 208 mV for OER and 195 mV for hydrogen evolution reaction (HER), respectively. More importantly, the morphology of NiFe-MOF-74 is nearly retained after 5000 cycles CV test for OER. The overall water splitting of as-prepared NiFe-MOF-74 electrode requires 1.58 V to achieve a current density of 10 mA cm−2, making it as a promising bifunctional electrocatalysts for water-splitting system.

Hierarchical Iron/Nickel-Based Sulfide Supported on Ni Foam As a Bifunctional Electrocatalyst for Efficient Overall Water Splitting

Water splitting, consisting of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), has received great attention owing to the potential to provide future sustainable and renewing energy source. However, the kinetically sluggish process of OER at anode and HER at cathode requires highly active electrocatalysts to accelerate the both electrode reactions. Currently, nickel-based catalysts are widely regarded as an effective electrocatalyst for OER due to their low cost, high stability, good redox properties, and high electrocatalytic performance. Herein, iron/nickel-based sulfide supported on Ni foam were simply synthesized using two step hydrothermal method and was used as a bifunctional electrocatalyst for OER and HER. The iron/nickel-based sulfide only require the low overpotentials of as smaller as 281 and 222 mV for HER and OER, respectively, at current density of 50 mA cm−2 in 1 M KOH. Assembled as an electrolyzer for overall water splitting, this bifunctional catalyst also indicates excellent low onset potential of only 1.41 V and deliver a current density of 10 mA cm−2 at a very low cell voltage of 1.59 V. The outstanding electrochemical performance of iron/nickel-based sulfide on Ni foam is mainly attributed to the synergistic effect of the binary metal system, leading to increasing the electroconductivity, active surface area, and intrinsic catalytic activity. These iron/nickel-based sulfide materials can be widely applied to fabricating efficient energy conversion and storage.