Partial Sulfidation Strategy to NiFe‐LDH@FeNi₂S₄ Heterostructure Enable High‐Performance Water/Seawater Oxidation

Abstract

The development of a high-performance electrocatalyst for oxygen evolution reaction (OER) is imperative but challenging. Here, a partial sulfidation route to construct Ni 2 Fe-LDH/FeNi 2 S 4 heterostructure on nickel foam (Ni 2 Fe-LDH/ FeNi 2 S 4 /NF) by adjusting the hydrothermal duration is reported. The heterostructures afford abundant hydroxide/sulfide interfaces that offer plentiful active sites, rapid charge and mass transfer, favorable adsorption energy to oxygenated species (OH − and OOH) evidenced by the density functional theory calculations, which synergistically boost the alkaline water oxidation. In the 1.0 m KOH solution, Ni 2 Fe-LDH/FeNi 2 S 4 /NF exhibits an excellent OER catalytic activity with a much smaller overpotential (240 mV) to reach the current density of 100 mA cm −2 than single-phase Ni 2 Fe-LDH/NF (279 mV) or FeNi 2 S 4 /NF (271 mV). More impressively, 2000 cycles of cyclic voltammetry scan for water oxidation results in the formation of a sulfate layer over the catalyst. The corresponding post-catalyst demonstrates better OER activity and durability than the initial one in the alkaline simulated seawater electrolyte. The post-Ni 2 Fe-LDH/FeNi 2 S 4 /NF delivers smaller overpotential (250 mV) at 100 mA cm −2 and longer stability time than the original form (260 mV). The post-formed sulfate passivating layer is responsible for the outstanding corrosion resistance of the salty-water oxidation anode since it can effectively repel chloride.

Recent advances in transition metal‐based electrocatalysts for seawater electrolysis

“…Typically, S species can convert to sulfate passivating layers during the OER, which play an important role in corrosion resistance. Guided by this, Tan et al designed and synthesized NiFe‐LDH@FeNi 2 S 4 with partial sulfidation strategy 104 . During the OER in the anode, the in‐situ conversion of sulfate layer shows repulsion to chloride ions, thus leading to improved stability.…”

“…Guided by this, Tan et al designed and synthesized NiFe-LDH@FeNi 2 S 4 with partial sulfidation strategy. 104 During the OER in the anode, the in-situ conversion of sulfate layer shows repulsion to chloride ions, thus leading to improved stability. In addition, benefiting from the partial sulfidation strategy, such formed heterostructure was characterized with abundant active sites, large surface areas, and accelerated electrons transfer.…”

MnOx Film-Coated NiFe-LDH Nanosheets on Ni Foam as Selective Oxygen Evolution Electrocatalysts for Alkaline Seawater Oxidation

“…Electrochemical water splitting has been recognized as the lowcarbon technology with the most potential to yield highly caloric hydrogen while cooperatively utilizing intermittent energy from renewables such as wind, solar, etc. 1,2 In this energy conversion process, the oxygen evolution reaction (OER) half-reaction is the bottleneck because this sluggish pathway needs a high potential to activate, which determines the overall electrolysis efficiency. 3−5 Another serious issue that remains in water electrolysis is the use of freshwater in both the laboratory and the scale-up production.…”

“…Electrochemical water splitting has been recognized as the low-carbon technology with the most potential to yield highly caloric hydrogen while cooperatively utilizing intermittent energy from renewables such as wind, solar, etc. , In this energy conversion process, the oxygen evolution reaction (OER) half-reaction is the bottleneck because this sluggish pathway needs a high potential to activate, which determines the overall electrolysis efficiency. − Another serious issue that remains in water electrolysis is the use of freshwater in both the laboratory and the scale-up production. However, it would be a grand challenge for practical electrolyzers because freshwater is a “rare resource” in many zones of the world albeit for daily drinking. , Being an abundant reserve (>96% of the global water body), seawater is undoubtedly defined as an almost inexhaustible water feedstock for water electrolysis .…”

“…In particular, NiFe-LDH has nearly been demonstrated as the most efficient OER catalyst and even used as a benchmark in alkaline electrolytes. − Moreover, various strategies have been adopted to fabricate NiFe-LDH composites that can enhance their OER activities in Cl – -containing solutions. For example, S-(Ni,Fe)­OOH, Ni/NiS x /NiFe hydroxide, NiFe-LDH/FeOOH, and Ni 2 Fe-LDH/FeNi 2 S 4 have displayed excellent OER activity in alkalized saline water. Despite some achievements in anodic electrodes, developing a highly active and stable OER-selective catalyst for seawater electrolysis remains challenging because the aggressive corrosion from Cl – ions would decay the catalyst.…”