Phosphorus‐Modified Amorphous High‐Entropy CoFeNiCrMn Compound as High‐Performance Electrocatalyst for Hydrazine‐Assisted Water Electrolysis

Abstract

Exploiting highly active and bifunctional catalysts for both hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR) is a prerequisite for the hydrogen acquisition. High‐entropy materials have received widespread attention in catalysis, but the high‐performance bifunctional electrodes are still lacking. Herein, a novel P‐modified amorphous high‐entropy CoFeNiCrMn compound is developed on nickel foam (NF) by one‐step electrodeposition strategy. The achieved CoFeNiCrMnP/NF delivers remarkable HER and HzOR performance, where the overpotentials as low as 51 and 268 mV are realized at 100 mA cm−2. The improved cell voltage of 91 mV is further demonstrated at 100 mA cm−2 by assessing CoFeNiCrMnP/NF in the constructed hydrazine‐assisted water electrolyser, which is almost 1.54 V lower than the HER||OER system. Experimental results confirm the important role of each element in regulating the bifuncational performance of high‐entropy catalysts. The main influencing elements seem to be Fe and Ni for HER, while the P‐modification and Cr metal may contribute a lot for HzOR. These synergistic advantages help to lower the energy barriers and improve the reaction kinetics, resulting in the excellent bifunctional activity of the CoFeNiCrMnP/NF. The work offers a feasible strategy to develop self‐supporting electrode with high‐entropy materials for overall water splitting.

Hydrothermal Prepared Bramble-like Double Arrays NiCo2S4 Bifunctional Electrocatalysts for High-Efficiency Water Splitting

“…From the positive scan LSV curves in Figure SI 11, the NiCo 2 S 4 /NF catalyst had the highest OER value with an overpotential of 203 mV at 10 mA cm –2 current density, which was better than noble metal RuO 2 , while the OER value of the NiCo 2 (OH) X /NF electrode was slightly higher than that of the Ni 3 S 2 /NF, which suggested that the incorporation of Co + significantly impacted the OER process. The OER of NiCo 2 S 4 /NF catalyst was significantly higher than that of the NiCo 2 (OH) X /NF precursor and Ni 3 S 2 /NF electrode without added Co + , which further proved that the introduction of Co + and sulfidation treatment enhanced the OER performance of the generated NiCo 2 S 4 /NF . In Figure b, we analyzed their Tafel slopes at the OER, and the tower slope of the NiCo 2 S 4 /NF electrocatalyst was 54 mV dec –1 , which was better than the noble metal RuO 2 at 67 mV dec –1 and superior to the NiCo 2 (OH) X /NF and Ni 3 S 2 /NF.…”

“…34 This is consistent with the NiCo 2 S 4 / NF electrode's dual nanowire structure with high electron transport, and the high electron transport, high catalytically active area, and intrinsic catalytic activity of the NiCo 2 S 4 /NF electrode result in high catalytic efficiency. 35,36 The stability measurements were also performed, as shown in Figure 4f, tested under 5000 CV cycles with a 72 h examination at a steady current of 10 mA cm −2 , which revealed no appreciable current decrease. In order to investigate the microstructural changes and stability of the electrocatalysts after HER tests, SEM, XRD, and XRS tests were also performed.…”

Hierarchical Cobalt–Nickel Phosphide/Molybdenum Disulfide Hybrid Electrocatalyst Triggering Efficient Hydrogen Generation in a Wider pH Range

“…This is consistent with the minimal interface transfer resistance of CoP/Ni 2 P/MoS 2 –CC from electrochemical impedance spectroscopy (Figure c). In addition, the C dl value of CoP/Ni 2 P/MoS 2 –CC is about 35 mF cm –2 (Figure d and Figure S7), which is higher than that for NiCo Pre/MoS 2 –CC (30 mF cm –2 ) and MoS 2 –CC (23 mF cm –2 ), suggesting a larger surface area toward more active sites during electrolysis. − …”

Interface Engineering of a Hierarchical P-Modified Co/Ni3P Heterostructure for Highly Efficient Water Electrolysis Coupled with Hydrazine Degradation

“…The intrinsic sluggish kinetics of HzOR involves multiple electron transfer and complex evolution pathways, necessitating that elaborate design of advanced materials for HzOR is significant to decrease the energy barrier and accelerate the reaction rate. – Over the past few years, various regulation strategies, such as interface engineering, vacancy design, doping, or morphology regulation, have been developed to promote the electrocatalytic activity of transition metal (TM)-based catalysts (alloy, sulfides, oxyhydroxides, phosphides, and nitrides). – Among them, the construction of TM-based heterostructured electrocatalysts is gradually emerging as one of the important regulatory strategies due to their tunable electronic structures, multiple metal centers, and abundant heterogeneous interfaces. For example, a copper–nickel nitride (Cu 4 N/Ni 3 N) prepared by Mai’s group exhibits an extremely low voltage of 0.24 V at 10 mA cm –2 as well as excellent stability for the hybrid water electrolyzer .…”