Bifunctional Electrocatalysts for Overall Water Splitting from an Iron/Nickel‐Based Bimetallic Metal–Organic Framework/Dicyandiamide Composite

Abstract

Pyrolysis of a bimetallic metal-organic framework (MIL-88-Fe/Ni)-dicyandiamide composite yield a Fe and Ni containing carbonaceous material, which is an efficient bifunctional electrocatalyst for overall water splitting. FeNi and NiFe O are found as metallic and metal oxide compounds closely embedded in an N-doped carbon-carbon nanotube matrix. This hybrid catalyst (Fe-Ni@NC-CNTs) significantly promotes the charge transfer efficiency and restrains the corrosion of the metallic catalysts, which is shown in a high OER and HER activity with an overpotential of 274 and 202 mV, respectively at 10 mA cm in alkaline solution. When this bifunctional catalyst was further used for H and O production in an electrochemical water-splitting unit, it can operate in ambient conditions with a competitive gas production rate of 1.15 and 0.57 μL s for hydrogen and oxygen, respectively, showing its potential for practical applications.

Ultrathin Ni(0)‐Embedded Ni(OH)2 Heterostructured Nanosheets with Enhanced Electrochemical Overall Water Splitting

“…For example, Ni‐based sulfides and phosphides were synthesized for the electrocatalytic HER, and Ni‐based oxides and hydroxides exhibited electrochemical oxygen evolution activities . Since the overall water splitting is critical in the practical application, it is desired to develop bifunctional electrocatalysts . Recently, several Ni‐based nanomaterials have been prepared and exhibited bifunctional electrocatalytic activities in HER and OER .…”

Cobalt‐Exchanged Poly(Heptazine Imides) as Transition Metal–Nx Electrocatalysts for the Oxygen Evolution Reaction

“…In this process, the oxygen evolution reaction (OER) is the more challenging half‐reaction, due to its slow kinetics, which stems from a four‐electron oxidation process. Indeed, the slow progress in optimizing this half‐reaction has largely hindered the development of overall water splitting devices . In addition, the so far best‐performing OER catalysts are based on noble metals (e.g., Ir and Ru), for which the high cost and scarcity limit their utilization especially in large‐scale applications .…”

Importance of Electrocatalyst Morphology for the Oxygen Reduction Reaction

“…The synergistic effect between confined metal or metal oxide NPs and N−C nanotubes affords the high ORR activity and fast electron/mass transfer. Recently, M−N−C materials with metal NPs embedded at the tips of N−C nanotubes were reported . The confined metal NPs at the tips of N‐doped CNTs can increase the density of state (DOS) near the Fermi level and decrease the work function, which finally improve the electrocatalytic activity of the ORR …”

“…Recently, MÀ NÀ C materials with metal NPs embedded at the tips of NÀ C nanotubes were reported. [86][87][88] The confined metal NPs at the tips of N-doped CNTs can increase the density of state (DOS) near the Fermi level and decrease the work function, which finally improve the electrocatalytic activity of the ORR. [86] More recently, Liang et al prepared a novel 1D MÀ NÀ C material with chiral carbonaceous nanotubes (CCNTs) as the support ( Figure 5).…”

“…Similarly, Zhao et al reported FeNi 3 and NiFe 2 O 4 embedded N-doped carbon-CNTs (Fe-Ni@NC-CNTs) based on the bimetallic MOF (MIL-88-Fe/ Ni). [88] Therefore, the efficient electrochemical activity of this kind of MD MÀ NÀ C materials is mainly ascribed to the high conductivity and abundant active sites. Figure 10.…”