Ultra‐Fast In Situ Reconstructed Nickel (Oxy)Hydroxide Nanoparticle Crosslinked Structure for Super‐Efficient Alkaline Water Electrolysis by Sacrificing Template Strategy

Abstract

The rapid construction of water electrolysis catalysts by a sacrificing template in an electrochemical environment is rarely a concern. Herein, using a fluorine‐rich (F‐rich) nickel fluoride (NiF2) grown on nickel foam (NF) as a sacrificial template, a highly effective alkaline catalyst is designed. In terms of in situ reassembling, the NiF2 template can be transformed into nickel hydroxide (Ni(OH)2) in hydrogen evolution reaction (HER) and nickel oxyhydroxide (NiOOH) in oxygen evolution reaction (OER), respectively, after only 100 CV cycles, on account of the rapid ion exchange of F− and OH− in an electrochemical environment. Due to the presence of nanocatalytic units, abundant lattice defects, and porous large specific surface structures caused by the reconstruction, it only takes low overpotentials of 57 mV for HER and 228 mV for OER (@10 mA cm−2), with outstanding stability up to 15 d (@100 mA cm−2). Consequently, only a low cell voltage of 1.53 V (@10 mA cm−2) is needed for overall water splitting, superior to commercial noble metal catalysts as benchmarks. Meanwhile, it can output stable current densities of 10, 100, and 500 mA cm−2 approaching 10 d under constant cell voltages of 1.55, 2.0, and 2.5 V, respectively.

Unlocking Catalytic Potential: Encasing CoP Nanoparticles within Mesoporous CoFeP Nanocubes for Enhanced Oxygen Evolution Reaction

“…Linear sweep voltammetry curves show that the OER activity of the CoP/CoFeP catalyst first increases and then decreases over continuous electrochemical cycling, which indicates the dynamic structural evolution reconstruction and the in situ generation of catalytic species under anodic conditions (Figure S26). Moreover, the potential changes at a current density of 10 mA cm –2 clearly show the reconstruction process in only a few CV cycles. Moreover, the OER activity of CoP/CoFeP is superior to those of the hollow CoFeP and ZIF-67/CoFe PBA (synthesized counterpart; Figure d).…”

Bifunctional Electrocatalysts for Overall and Hybrid Water Splitting

“…By scanning the sample through 2θ angles, all possible directions of diffractions of the lattice can be obtained. XRD is thus an excellent technique to reveal the crystallographic information on materials, such as the cell parameters, strain, and microstructure, and can be employed to identify the crystalline phase evolution of the underlying electrocatalysts before and after the electrocatalytic processes. − For instance, our group detected the reconstruction of Ni 2 P/Ni/NF bifunctional electrocatalyst after OER by ex situ XRD (Figure a) . Additional peaks assignable to NiO were observed for the post-OER sample, suggesting the electrochemical oxidation of Ni 2 P/Ni/NF.…”

F-doped NiOOH derived from progressive reconstruction for efficient and durable water oxidation

“…17,18 According to recent research, fluorides and fluoride-containing compounds are highly susceptible to structural reconstruction under alkaline OER conditions because of the strong hydrophilic characteristics and quick ion exchange capacity. 19–21 Therefore, a deeper in situ transformation that accompanies more generation of highly-active MOOH species can be realized if fluorides are used as precatalysts. Researchers have confirmed that most of the fluorine ions electrochemically dissolve into the electrolyte during the deep reconstruction.…”

“…22,23 Nevertheless, the actual effect of residual fluorine ions on the OER, whether adsorbed on the surface of reconstructed products or doped in the MOOH like chalcogen, 24,25 is still ambiguous. More importantly, fluorides could undergo a fast reconstruction process accompanied by a high catalyst dissolution rate, 19,26 which is detrimental to catalytic stability. Actually, both experimental results and theoretical calculations have revealed that some pre-catalysts may experience severe structural collapse during the drastic reconstruction, resulting in unsatisfactory OER stability, which is attributed to the volumetric expansion effect and/or crystal structure mismatch between pre-catalysts and reconstructed products.…”