A Self‐Reconstructed Bifunctional Electrocatalyst of Pseudo‐Amorphous Nickel Carbide @ Iron Oxide Network for Seawater Splitting

Abstract

Here, a sol-gel method is used to prepare a Prussian blue analogue (NiFe-PBA) precursor with a 2D network, which is further annealed to an Fe 3 O 4 /NiC x composite (NiFe-PBA-gel-cal), inheriting the ultrahigh specific surface area of the parent structure. When the composite is used as both anode and cathode catalyst for overall water splitting, it requires low voltages of 1.57 and 1.66 V to provide a current density of 100 mA cm −2 in alkaline freshwater and simulated seawater, respectively, exhibiting no obvious attenuation over a 50 h test. Operando Raman spectroscopy and X-ray photoelectron spectroscopy indicate that NiOOH 2-x active species containing high-valence Ni 3+ /Ni 4+ are in situ generated from NiC x during the water oxidation. Density functional theory calculations combined with ligand field theory reveal that the role of high valence states of Ni is to trigger the production of localized O 2p electron holes, acting as electrophilic centers for the activation of redox reactions for oxygen evolution reaction. After hydrogen evolution reaction, a series of ex situ and in situ investigations indicate the reduction from Fe 3+ to Fe 2+ and the evolution of Ni(OH) 2 are the origin of the high activity.

Heterostructured Core–Shell Ni–Co@Fe–Co Nanoboxes of Prussian Blue Analogues for Efficient Electrocatalytic Hydrogen Evolution from Alkaline Seawater

“…The two peaks at 2134 and 2145 cm –1 in the Raman spectra are attributed to the stretching vibrations of C≡N and denoted as peak A and peak B, respectively ( Figure 5 a,b), which are sensitive to the oxidation states of coordinated cobalt ions (Co III and Co II , respectively). 4 , 41 , 42 It is observed that the overall intensity of the peak decreases slightly with the applied potential, indicating some loss of catalyst. The intensity of peak A significantly decreases compared to that of peak B, suggesting that Co 3+ is reduced.…”

“…The stability of Ni–Co@Fe–Co PBA in alkaline simulated seawater was also tested by chronoamperometry measurement at an applied potential of −0.23 V versus RHE (Figure S7), and the retention rate after 24 h test was 98.4%, which is slightly inferior to the durability in alkaline freshwater. The lower HER activity of the PBA catalysts in alkaline simulated seawater compared to alkaline freshwater is due to Cl – -induced chlorine evolution reaction, hypochlorite formation, and chloride corrosion under alkaline conditions. , …”

“…The lower HER activity of the PBA catalysts in alkaline simulated seawater compared to alkaline freshwater is due to Cl – -induced chlorine evolution reaction, hypochlorite formation, and chloride corrosion under alkaline conditions. 8 , 41 …”

Recent advances in transition metal‐based electrocatalysts for seawater electrolysis

“…Typically, the obtained VS 2 nanosheets were characterized as well dispersibility without the inter‐sheet agglomeration due to the important role of 2D V 2 C. Consequently, such VS 2 @V 2 C exhibited excellent HER performance and stability for full pH range seawater splitting. For instance, Zhang et al synthesized a Fe 3 O 4 /NiC x composite toward good overall water‐splitting performance in seawater by a sol‐gel method, in which chronoamperometry test demonstrated an excellent durability 52 …”

“…For instance, Zhang et al synthesized a Fe 3 O 4 /NiC x composite toward good overall watersplitting performance in seawater by a sol-gel method, in which chronoamperometry test demonstrated an excellent durability. 52 In addition to the well dispersibility and stability provided by the 2D TMCs, 2D carbon-based protective layer can effective protect the active catalyst from the harsh environment in seawater. Bu et al synthesized core-shell NiMo@C 3 N 5 featured with 2D C 3 N 5 shells, which could serve as robust HER catalyst in seawater.…”