In Situ Synthesis of Superhydrophilic Amorphous NiFe Prussian Blue Analogues for the Oxygen Evolution Reaction at a High Current Density

Abstract

Synthesis of efficient and low-cost catalysts for the oxygen evolution reaction (OER) is a pivotal process for large-scale electrocatalytic water splitting to produce hydrogen. Prussian blue analogues (PBAs) prepared by the conventional co-precipitation method, with a less active site density and a poor electrical transport, are often used as precursors for further preparation of PBA derivatives, such as metal oxides, metal alloys, metal phosphides, and so on, due to their poor OER activity. In this report, controllable synthesis of NiFe PBA with Fe2O3 byproducts on a Ni foam substrate was achieved through a facile one-step hydrothermal reaction by adjusting the amount of urea and potassium ferricyanide. After chemical etching and electrochemical activation, NiFe PBA was entirely transformed into amorphous superhydrophilic NiFe PBA (denoted a-NiHCF), which exhibited a remarkable OER performance at a large current density. To drive high current densities of 400 and 800 mA cm–2, only ultralow overpotentials of 280 and 309 mV were required, respectively, which far exceed many recently reported OER catalysts. The superior performance can be attributed to the following: (1) in situ growth on a metal foam substrate can improve the structural stability and provide a faster charge transfer as well as oxygen bubble release; (2) chemical etching allows exposing more surface active sites; (3) an electrochemical activation-induced amorphous surface possesses a larger Brunauer–Emmett–Teller surface area, more high-valent oxidation states, and higher intrinsic OER activity; and (4) the superhydrophilic surface structure is conducive to the adsorption of water molecules. These advantages make a-NiHCF a promising candidate for application in the field of electrocatalytic water splitting.

One-pot hydrothermal synthesis of Co–Ni hexacyanoferrate nanocuboids on Ni-foam as efficient catalysts for oxygen evolution and urea oxidation reactions

“…In the PBA crystal system, the N-coordinated high-spin P cations and C-coordinated low-spin R cations are interlinked with C≡N bridges, forming an open face-centered cubic structure that provides distinctive advantages such as high porosity, large specific surface area, and tunable metal active sites, which are beneficial for various applications, such as catalysis, energy storage, and sensors [33][34][35][36][37]. Currently, among the wide selection of PBA family, the metal hexacyanoferrates (HCFs), in which lowspin R cations are replaced with Fe and high-spin cations are replaced with transition metal ions (mostly Co, Ni, Cu, and Zn), are of interest owing to their chemical stability over a wide pH range, tunable physicochemical properties, and catalytic activities, which are comparable to those of metal oxides [31,38]. Despite these technical advantages, metal HCFs still suffer from low current densities and mechanical resistance owing to their conductivity and poor interfacial bonding with the electrode surfaces; subsequently, limiting their application.…”

3D Spatial Combination of CN Vacancy‐Mediated NiFe‐PBA with N‐Doped Carbon Nanofibers Network Toward Free‐Standing Bifunctional Electrode for Zn–Air Batteries

“…Many researchers have studied the microstructure and/or catalytic mechanism of PBAs to further improve the catalytic activity. [ 13–17 ] For example, Galan‐Mascaros et al. [ 18 ] verified that Co‐Fe PBA catalyst exhibits more efficient and stable catalytic performance for OER after chemical etching treatment.…”

“…Many researchers have studied the microstructure and/or catalytic mechanism of PBAs to further improve the catalytic activity. [13][14][15][16][17] For example, Galan-Mascaros et al [18] verified that Co-Fe PBA catalyst exhibits more efficient and stable catalytic performance for OER after chemical etching treatment. Thereinto, manipulating the defect chemistry is a popular and efficient strategy to tune the catalytic activity of materials.…”

Three‐Dimensional Porous MnCo2S4 Microrugby Balls Supported on Carbon Cloth for Efficient Oxygen Evolution Reaction

“…Hence, the development of non-noble metals with high activity and durable stability is of great significance. [6] In recent years, transition metal base compounds (oxides, [7] nitrides, [8] sulphides, [9] phosphating [10] compounds, etc.) have been extensively considered as promising OER electrocatalysts.…”

“…The addition of catalyst can effectively reduce the overpotential in the process of water electrolysis, which can reduce energy consumption and save energy to a certain extent. Hence, the development of non‐noble metals with high activity and durable stability is of great significance [6] …”