Hierarchical Core‐Shell N‐Doped Carbon@FeP₄‐CoP Arrays as Robust Bifunctional Electrocatalysts for Overall Water Splitting at High Current Density

Abstract

Exploring non‐precious metal‐based electrocatalysts at high current density and stability is an urgent issue for sustainable H2 production. Here, hierarchical core‐shell N‐doped carbon encapsulated array‐like FeP4 and CoP active components have been fabricated in situ on the surface of nickel foam (NC@FeP4‐CoP/NF) by etching sheet‐like ZIF‐67 arrays, Prussian analog formation, and phosphating in turns. The crystallinity, hierarchical heterostructure, and chemical state have been carefully discussed. Electrochemical studies demonstrate that the catalyst displays excellent electrocatalytic activity and durability in electrochemical oxygen evolution reaction (η20 = 218 mV) and hydrogen evolution reaction (η10 = 116 mV), better than most previously reported bifunctional catalysts. Moreover, the bifunctional catalyst only needs 1.72 and 1.80 V cell voltages at 500 and 1000 mA cm−2 respectively, together with a good catalytic stability at 500 mA cm−2 for 48 h, implying potential commercialization prospects. This excellent electrocatalytic performance is mainly attributed to the distinctive hierarchical structure as well as core‐shell NC encapsulated FeP4‐CoP active sites, which can enhance the charge transport rate, inhibit the exfoliation of the active materials, provide a larger active surface area, and facilitate electrolyte diffusion and gas release.

Boosting Electrocatalytic Oxygen Evolution: Superhydrophilic/Superaerophobic Hierarchical Nanoneedle/Microflower Arrays of CexCo3–xO4 with Oxygen Vacancies

“…The porosity and surface area of Ce 0.12 Co 2.88 O 4 and Co 3 O 4 were acquired by the method of N 2 adsorption–desorption isotherms. In Figure S8a, the obtained curve was consistent with a typical type III isotherm with a hysteresis loop . Ce 0.12 Co 2.88 O 4 has larger Brunauer–Emmett–Teller (BET) surface area (78.26 m 2 g –1 ) and pore volume (0.195 cm 3 g –1 ) than pristine Co 3 O 4 (61.74 m 2 g –1 and 0.158 cm 3 g –1 , respectively).…”

“…In Figure S8a, the obtained curve was consistent with a typical type III isotherm with a hysteresis loop. 55 Ce 0.12 Co 2.88 O 4 has larger Brunauer−Emmett−Teller (BET) surface area (78.26 m 2 g −1 ) and pore volume (0.195 cm 3 g −1 ) than pristine Co 3 O 4 (61.74 m 2 g −1 and 0.158 cm 3 g −1 , respectively). In addition, the average pore size of Ce 0.12 Co 2.88 O 4 (10.53 nm) was reduced slightly compared to Co 3 O 4 (11.10 nm) (Figure S8b).…”

Co–Fe–P Nanosheet Arrays as a Highly Synergistic and Efficient Electrocatalyst for Oxygen Evolution Reaction

“…O is also found in the XPS spectrum of Co-Fe-P/CC, which is a commonly reported phenomenon induced by the oxidation of active Co-P and Fe-P by atmospheric oxygen under ambient condition. [30,31,41] The Co 2p spectrum is deconvoluted into peaks of Co-O at 796.9 eV, Co-P at 794.0 and 779.0 eV, and their satellite peaks at 802.8 and 784.9 eV, respectively (Figure 3b); the P 2p spectrum is deconvoluted into peaks of P 2p1/2 at 130.7 eV, P 2p3/2 at 129.8 eV and P-O at 134.3 eV (Figure 3d). The peak of Co-P (794.0 and 779.0 eV) and Fe-P (707.4 eV) confirm the existence of Co-P and Fe-P in Co-Fe-P/CC.…”

“…The peak of Co-P (794.0 and 779.0 eV) and Fe-P (707.4 eV) confirm the existence of Co-P and Fe-P in Co-Fe-P/CC. The peaks corresponding to P-O, Co-O and Fe-O bonds indicates that Co-Fe-P is prone to oxidation by atmosphere oxygen under ambient condition, which is due to the active chemical properties of Co-P and Fe-P. [30,31,41] Moreover, as compared with the spectra of with Co-P/CC and Fe-P/CC (Figure 3d; also see their XRD patterns and SEM images in Figure S11-S13), the XPS spectra of Co-Fe-P/CC show a positive shift of 0.6 eV in the Co-P peak position, and a negative shift of 0.8 eV in the Fe-P peak position, which thus clearly indicates the electron transfer from Co to Fe in Co-Fe-P and the synergistic effects between Co and Fe. Such electron transfer from Co to Fe leads to the generation of more Co 3+ in high-valence state (cf.…”

Engineering transition metal catalysts for large-current-density water splitting

“…63 For example, Yang et al have adopted a metal-organic framework (MOF) mediated method to realize the successful fabrication of N-doped carbon encapsulated array-like FeP 4 and CoP on the surface of NF. 64 On the one hand, the introduction NF can largely enhance the electrical conductivity to boost the electron transfer during electrochemical reactions. On the other hand, nano-level dispersion of FeP 4 and CoP generates a sufficient interface, which will modify the electronic structure of the catalyst to enhance the intrinsic activity of the catalyst, thereby leading to outstanding electrocatalytic OER performance.…”