Integrated Bifunctional Electrodes Based on Amorphous Co–Ni–S Nanoflake Arrays with Atomic Dispersity of Active Sites for Overall Water Splitting

Abstract

Fabrication of amorphous electrocatalysts without noble metals for cost-effective full water splitting is highly desired but remains a substantial challenge. In the present work, we report a facile strategy for exploring integrated bifunctional electrocatalysts based on amorphous cobalt/nickel sulfide nanoflake arrays self-supported on carbon cloth, by tailoring competitive coordination of metal ions between glucose and 2-aminoterephthalic acid. Ultrahigh dispersion of binary metal active sites with balanced atomic distribution enables the optimization of catalytic properties for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in an alkaline solution. The obtained catalyst exhibits remarkably enhanced OER and HER activities as compared with its oxide counterpart and analogues with different Co/Ni ratios. It requires overpotentials of 296 and 192 mV to deliver a current density of 10 mA cm −2 for the OER and HER, respectively; it retains 96.6 and 96.9% activity after 32 h of OER and 36 h of HER tests at 10 mA cm −2 , respectively. As directly used an anode and a cathode in an alkaline electrolyzer, a low cell voltage of 1.60 V could endow a water splitting current of 10 mA cm −2 , outperforming the benchmark RuO 2 and Pt/C-based electrolyzer at 1.72 V@10 mA cm −2 . The current synthetic strategy may provide more opportunities for the design and direct synthesis of amorphous catalysts for overall water splitting and beyond.

Hierarchically Self-Supporting Phosphorus-Doped CoMoO4 Nanoflowers Arrays toward Efficient Hydrogen Evolution Reaction

“…The frequent occurrence of climate change and resource shortages have drawn widespread attention to hydrogen energy as a clean and sustainable source. − Among the existing hydrogen production technologies, electrocatalytic hydrogen evolution reaction (HER) stands out in terms of being convenient, environmentally friendly, and highly efficient. − The most widely accepted electrocatalysts are platinum, , rubidium, , rhodium, and iridium owing to their low overpotentials, Tafel slopes, and good stability. The application of precious metals as electrocatalysts is restricted by their high cost and scarcity of elements. − In light of this fact, nonprecious metal catalysts have been extensively investigated. A number of catalysts with excellent performance have been proposed, including phosphides, − sulfides, − oxides, − hydroxides, , carbides, , and so on, which are expected to be promising substitutes for precious metal electrocatalysts due to their low cost and simple preparation methods. − …”

NiCo2O4 nanoparticles rich in oxygen vacancies: Salt-Assisted preparation and boosted water splitting

“…Table 1 shows the summary of HER and OER activity of some typical electrocatalysts reported in the literatures. Obviously, the HER and OER catalytic performance of NiCo 2 O 4 -2KCl is comparable to that of the recently-developed HER/OER bifunctional catalysts, although the highly conductive substrates were not applied to support as the binder-free electrodes, such as carbon cloth ( Dong et al, 2022 ), Ni foams ( Ha et al, 2019 ; Du et al, 2021 ; He et al, 2021 ), etc.…”

“…However, they are limited in large-scale production due to high costs and low reserves. In recent years, various Co-based electrocatalysts, such as phosphides (Zhang et al, 2022b), carbides (Wang et al, 2021), oxides (Jung et al, 2021) and sulfides (Dong et al, 2022) have been developed and applied for water splitting to hydrogen. Among them, NiCo 2 O 4 spinel oxide has shown great application potentials in many energy storage and conversion systems (Chen et al, 2018;Ranjani et al, 2018), because of simple preparation methods, high stability against corrosion in electrochemical systems, and, more importantly, high electrochemical activity (Ha et al, 2019;Du et al, 2021;Sun et al, 2021).…”

Crystalline–Amorphous Ni3S2–NiMoO4 Heterostructure for Durable Urea Electrolysis-Assisted Hydrogen Production at High Current Density

“…Combining the structural advantages of crystalline and amorphous catalysts to design crystalline–amorphous heterostructure catalysts could retain their inherent properties. Such materials can provide more defects as unsaturated active sites to show better activity compared with crystalline catalysts. , Besides, this novel structure with strong interface interactions would cause charge redistribution to optimize the electron structure. , Wu and Li et al , pointed out that the crystalline–amorphous heterostructure catalysts exhibit high activity by optimizing H atom desorption and H 2 O adsorption, which is confirmed by density functional theory (DFT) calculation. Huang et al reported that the crystalline–amorphous interfaces can provide more active sites, accompanied by boosting the absorption of urea molecules and breaking the chemical bonds to enhance the UOR activity.…”