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Article

Nickel Foam-Supported FeP Encapsulated in N, P Co-Doped Carbon Matrix for Efficient Electrocatalytic Hydrogen Evolution

by
Jianguo Zhong
1,
Ting Zhang
1,*,
Jianqiang Tian
1,
Wei Gao
2 and
Yuxin Wang
1,*
1
School of Materials Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212114, China
2
Department of Chemical and Materials Engineering, Faculty of Engineering, The University of Auckland, Auckland 1142, New Zealand
*
Authors to whom correspondence should be addressed.
Inorganics 2024, 12(11), 291; https://doi.org/10.3390/inorganics12110291
Submission received: 14 September 2024 / Revised: 23 October 2024 / Accepted: 4 November 2024 / Published: 7 November 2024
(This article belongs to the Special Issue Featured Papers in Inorganic Materials 2024)
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Abstract

:
Transition metal phosphides (TMPs) show great potential as catalysts for the hydrogen evolution reaction (HER). FeP stands out as an efficient and cost-effective non-noble metal-based HER catalyst. However, FeP tends to aggregate and suffer from instability during the reaction. To tackle these challenges, we developed an efficient and straightforward approach to load metal-organic framework-derived N/P co-doped carbon-encapsulated FeP nanoparticles onto a nickel foam substrate (FeP@NPC/NF-450). This catalyst exhibits exceptional HER activity in 0.5 M H2SO4 and 1.0 M KOH solutions, with overpotentials of 68.3 mV and 106.1 mV at a current density of 10 mA cm−2, respectively. Furthermore, it demonstrates excellent stability with negligible decay over 48 h in both acidic and alkaline solutions. The outstanding hydrogen evolution catalytic performance of FeP@NPC/NF-450 is mainly due to the N, P co-doped carbon matrix, which safeguards the FeP nanoparticles from aggregation and surface oxidation. Consequently, this enhances the availability of active sites during the hydrogen evolution reaction (HER), leading to improved stability. Moreover, introducing nickel foam offers a larger specific surface area and enhances charge transfer rates. This study provides a reference method for preparing stable and highly active electrocatalysts for hydrogen evolution.

Graphical Abstract

1. Introduction

With the increasing severity of environmental pollution and energy shortages, the development of sustainable clean energy has gradually gained the attention of various countries [1,2,3,4,5,6]. Over the past few decades, numerous renewable green energy sources, such as biomass, solar, wind, geothermal, and hydrogen, have been explored. Among these renewable energy sources, hydrogen energy stands out due to its high energy density, and clean, pollution-free characteristics [7,8]. Noble metal-based materials are typically considered efficient catalysts for electrochemical water splitting to produce hydrogen. However, their limited abundance on earth and high costs restricts the commercial application of noble metal-based catalysts. Using abundant non-noble metals on earth as catalysts for water electrolysis to produce hydrogen has become a research hotspot [9]. Various catalysts have been developed to advance non-noble metal-based hydrogen evolution reaction (HER) catalysts, including transition metal carbides [10,11], transition metal sulfides [12,13], transition metal nitrides [14,15], transition metal oxides [16,17], and transition metal phosphides [18,19].
Among the various transition metal-based catalysts, transition metal phosphides have garnered significant attention for their excellent electrocatalytic activity and affordability. Among all the other transition metals, due to the low price and high Earth abundance of Fe, FeP has attracted much attention due to the electrocatalytic HER performance in consideration of other nature resources. FeP-based catalysts are reported to have high levels of activity in wide pH ranges in both acid and alkaline electrolytes. However, the HER activity of FeP is still inferior to that of Pt-based catalysts, so enhancing FeP-based electrocatalytic activity is a substantial challenge [20]. Previously, numerous researchers have investigated FeP-based electrocatalysts. Wei and his team synthesized spindle-shaped Co-doped FeP supported on three-dimensional reduced graphene oxide using a hydrothermal method [21]. The synthesized catalyst demonstrated a low overpotential of 110.8 mV at a current density of 10 mA cm−2 in an acidic environment. Similarly, Jiang’s group constructed a hollow spherical heterostructure FeCo-P catalyst through a hydrothermal and phosphorization method [22]. The hollow spherical structure and the heterostructure between Co2P and FeP endowed the catalyst with a low overpotential of only 131 mV at a current density of 10 mA cm−2 in 1.0 M KOH. Despite these advances, the catalytic activity and stability of FeP are significantly limited by the slow charge transfer rate, the low number of active sites, and its high sensitivity to oxygen during water electrolysis. Metal-organic frameworks (MOFs), consisting of metal ions or clusters linked to organic ligands, have gained significant attention for their large specific surface area and high porosity [23]. Utilizing MOFs as templates has proven to be an effective strategy for preparing porous carbon/transition metal phosphides, transition metal oxides, and transition metal sulfides, which exhibit excellent catalytic performance [24].
To improve the electrocatalytic activity and stability of FeP, it is crucial to design a structure that maximizes the exposure of active sites while preventing catalyst aggregation and surface oxidation. Thus, it is essential to develop an efficient structure that keeps FeP nanoparticles separated during the reaction. Recently, carbon materials have been widely used to encapsulate FeP nanoparticles [25]. Carbon prevents FeP nanoparticles from aggregating during phosphorization and protects FeP electrocatalysts from oxidation during the hydrogen evolution reaction (HER) [26]. However, the intrinsic activity of carbon materials requires enhancement. The low intrinsic activity of carbon diminishes the electrocatalytic performance of carbon-coated FeP nanoparticles. Recent studies have revealed that nitrogen (N) doping in carbon matrices can create additional active sites for transition metal phosphide-based catalysts during the HER, significantly enhancing their overall performance. Also, nickel foam exhibits excellent conductivity, facilitating efficient electron transport during electrochemical reactions, thus improving catalytic performance [27]. Furthermore, the robust structure of nickel foam ensures good catalyst stability. It also allows direct electrochemical performance testing without needing binders, significantly saving time. The interaction between the nickel foam substrate and the catalyst can generate synergistic effects, further enhancing overall catalytic efficiency [28].
Inspired by these developments, we synthesized an N, P-doped carbon-coated FeP catalyst supported on nickel foam (NF). This catalyst was prepared by immersing nickel foam in a Fe-MOF solution, enabling successful loading of the MOF onto the nickel foam, followed by phosphorization in a tube furnace under an Ar atmosphere. The resulting FeP@NPC/NF catalyst exhibited excellent HER catalytic activity and stability in alkaline and acid mediums.

2. Result and Discussion

To avoid interference from the nickel foam substrate and the X-ray diffractometer sample holder, X-ray diffraction spectra were collected for FeP@NPC-T (T = 400 °C, 450 °C, 500 °C) and Fe2O3@NC after removing the nickel foam substrate. The X-ray diffraction spectra of samples subjected to different heat treatment temperatures exhibit similar main features, as shown in Figure 1. The diffraction peaks of the FeP@NPC/NF-T samples match well with those of FeP (PDF#01-071-2262). The diffraction peaks observed at 30.9°, 32.8°, 34.5°, 35.5°, 37.2°, 46.3°, 46.9°, 48.3°, 50.4°, 56.1°, and 59.6° correspond to the (020), (011), (220), (120), (111), (121), (220), (211), (130), (221), and (002) crystal planes of FeP (PDF#01-071-2262) [22], respectively. This indicates the successful synthesis of the FeP phase in the catalysts.
The morphology and structure of FeP@NPC/NF-400, FeP@NPC/NF-450, and FeP@NPC/NF-500 were examined using scanning electron microscopy (SEM), as shown in Figure 2a–i. The nickel foam surface is porous and smooth, providing ample space for catalyst growth and gas release channels, which helps mitigate the decline in catalytic performance. After loading FeP@NPC nanoparticles onto the nickel foam, the surface becomes rougher. The size of the nanoparticles in the catalysts enhanced due to the increase in the annealing temperature from 400 °C to 500 °C. Figure 2g presents the EDS elemental mapping of the FeP@NPC/NF-450 sample, indicating the presence and uniform distribution of Ni, Fe, P, N, and C elements within the catalyst, further confirming the successful synthesis of the FeP@NPC/NF catalyst.
Transmission electron microscopy (TEM) characterization of FeP@NPC/NF-450 exhibits a large number of small nanoparticles encapsulated by the matrix, as shown in Figure 3. The formation of the matrix could be attributed to the heat treatment of 2-methylimidazole. The d spacing of the crystalline fringe is 0.241 nm, indicating the formation of (111) in the FeP phase [29]. The TEM results exhibit that the FeP nanoparticles are encapsulated in the N, P-doped carbon matrix.
To further investigate the chemical composition and electronic properties of the FeP@NPC/NF-450 catalyst, an X-ray photoelectron spectroscopy (XPS) analysis was performed. Figure 4a shows the XPS spectra of the FeP@NPC/NF-450 catalyst. The Ni 2p XPS spectrum of FeP@NPC/450/NF exhibits six characteristic peaks, as shown in Figure 4b. The two peaks at 853.33 eV and 870.65 eV, corresponding to Ni 2p3/2 and Ni 2p1/2, are attributed to the presence of metallic Ni0, indicating that Ni primarily exists in its metallic form. The peaks at 856.81 eV and 874.01 eV are assigned to Ni-O, while the broad peaks at 861.93 eV and 880.32 eV correspond to satellite peaks [30,31]. The XPS spectrum of Fe 2p exhibits five characteristic peaks, as shown in Figure 4c. The two peaks at 706.27 eV and 719.07 eV, corresponding to Fe 2p3/2 and Fe 2p1/2, are attributed to the presence of Fe2+, while the peaks at 709.65 eV and 723.51 eV are attributed to Fe3+. The presence of both Fe2+ and Fe3+ is ascribed to the formation of Fe-O. The peak at 713.14 eV is associated with the formation of Fe-P bonds [32,33], consistent with the XRD results (Figure 4c). Figure 4d shows the high-resolution P 2p spectrum, which can be deconvoluted into three peaks: 129.85 eV (P 2p3/2) and 130.74 eV (P 2p3/2) corresponding to the formation of Fe-P bonds, and 134.50 eV attributed to P-O bonds formed by surface oxidation [34,35]. The N 1s spectrum can be resolved into three primary peaks, which correspond to graphitic N at 401.87 eV, pyrrolic N at 400.34 eV, and pyridinic N at 399.36 eV, as previously reported [36,37]. The incorporation of nitrogen into the carbon framework serves to both improve the catalyst’s conductivity and augment the quantity of active sites conducive to hydrogen generation [38]. The C 1s XPS spectrum (Figure 4f) shows a strong peak at 284.79 eV, corresponding to C=C bonds, along with peaks at 286.74 eV and 288.65 eV, representing C-N=O and O-N=O bonds, respectively, indicating successful nitrogen doping in the carbon matrix [39,40]. These analyses confirm the successful synthesis of the FeP@NPC/NF-450 catalyst.
The electrocatalytic performance of FeP@NPC/NF-450 during the hydrogen evolution reaction (HER) was tested in a 1.0 M KOH solution. The HER performance levels of Pt sheets, FeP@NPC/NF-400, FeP@NPC/NF-500, Fe2O3@NC/NF, and nickel foam were also analyzed for comparison. The linear sweep voltammetry (LSV) curves of the catalysts are shown in Figure 5a. The Pt sheet exhibited the lowest overpotential of 35.1 mV at a current density of 10 mA cm−2, demonstrating the highest HER performance [41]. Among the FeP@NPC/NF catalysts synthesized at different phosphorization temperatures and Fe2O3@NC/NF and nickel foam, FeP@NPC/NF-450 showed the highest HER activity. At a current density of 10 mA cm−2, the overpotential of FeP@NPC/NF-450 was only 106.1 mV, significantly lower than that of FeP@NPC/NF-400 (138.9 mV), FeP@NPC/NF-500 (142.9 mV), Fe2O3@NC/NF (201.1 mV), and nickel foam (177.8 mV). FeP nanoparticles are protected by the N, P-doped carbon matrix from aggregation, the mass transfer in the big bulk particles will be hindered. The HER properties will decrease with the increase in the annealing temperature to 500 °C. However, when the annealing temperature is under 450 °C, the crystal structure of FeP is weak in the XRD results, indicating that some of the Fe-MOF precursor is transferring to the FeP phase. According to the LSV results, FeP is the active site of the catalyst; the weak crystal structure of FeP will decrease the number of active sites during the reaction, thus hindering the HER properties of the catalyst.
To investigate the kinetics of the catalysts, their Tafel slopes were analyzed (Figure 5b). The Tafel slope of FeP@NPC/NF-450 was only 110.73 mV dec−1, significantly lower than those of FeP@NPC/NF-400 (135.10 mV dec−1), FeP@NPC/NF-500 (164.60 mV dec−1), Fe2O3@NC/NF (392.92 mV dec−1), and Ni foam (172.16 mV dec−1). This indicated that FeP@NPC/NF-450 exhibits the highest efficiency for hydrogen production, so we conducted a further analysis of the catalysts’ kinetics during the hydrogen evolution reaction (HER) process. Nyquist plots were obtained for FeP@NPC/NF-400, FeP@NPC/NF-450, FeP@NPC/NF-500, Fe2O3@NC/NF, and Ni foam, as depicted in Figure 5c. The efficiency of electron charge transfer within the catalysts is manifested by the diameter of the semicircles in the Nyquist plots, which is indicative of the charge transfer resistance (Rct) encountered during the reaction. The resistance at the interface between the electrolyte and the catalyst is termed as Rs [42]. Notably, FeP@NPC/NF-450 demonstrated the lowest internal resistance of 5.42 Ω cm−2, signifying its superior electron transfer efficiency compared to the other catalysts. This enhanced performance can be ascribed to the N- and P-doped carbon matrix, along with the nickel foam substrate, which effectively mitigates the aggregation of FeP nanoparticles during the annealing process. As a result, these structural features facilitate accelerated charge transfer between the active sites and the electrolyte.
To delve deeper into the hydrogen evolution reaction (HER) performance of the catalysts during hydrogen production, the double-layer capacitance (Cdl) was determined by conducting cyclic voltammetry scans at various sweep rates, spanning from 20 to 100 mV s−1. The Cdl values of FeP@NPC/NF-400, FeP@NPC/NF-450, FeP@NPC/NF-500, Fe2O3@NC/NF, and nickel foam was 3.28 mF cm−2, 6.70 mF cm−2, 2.38 mF cm−2, 1.19 mF cm−2, and 1.99 mF cm−2, respectively, as shown in Figure 5d. FeP@NPC/NF-450 exhibited the largest double-layer capacitance, significantly higher than that of the other catalysts studied. This suggests that encapsulation in the N and P-doped carbon matrix prevents the aggregation of FeP nanoparticles and facilitates the redistribution of electrons among N, P, and C, promoting the exposure of more active sites.
Assessing the stability of FeP@NPC/NF-450 during the hydrogen production process is of utmost importance. The stability of FeP@NPC/NF-450 was assessed by 1000 cyclic voltammetry scans and chronoamperometry tests. As shown in Figure 6a, after long-term testing over 1000 cycles, there was no significant change in the polarization curve compared to the catalyst before cycling. As depicted in Figure 6b, the current density of FeP@NPC/NF-450 remained almost unchanged after 48 h at 106.1 mV in the chronoamperometry test. Those results indicate that the catalyst’s structure remains stable in the reaction and Fe atoms do not leach out from the materials. The stability of FeP@NPC/NF-450 can be attributed to the encapsulation by the N and P co-doped carbon, which prevents the oxidation and corrosion of the FeP nanoparticles in 1.0 M KOH electrolyte [25].
Figure 7 showcases the hydrogen evolution reaction (HER) performance of the synthesized catalysts in an acidic electrolyte (0.5 M H2SO4). The linear sweep voltammetry (LSV) curves (Figure 7a) demonstrate that the HER catalytic activity of the FeP@NPC/NF-450 catalyst surpasses that of the other studied catalysts, second only to the Pt sheet. At a current density of 10 mA cm−2, the overpotentials of the FeP@NPC/NF-400, FeP@NPC/NF-450, FeP@NPC/NF-500, Fe2O3@NC/NF, Ni foam, and Pt sheet catalysts were 86.8 mV, 68.3 mV, 135.9 mV, 229.5 mV, 134.6 mV, and 33.5 mV, respectively. Figure 7b shows the Tafel slopes of the prepared catalysts, with the Tafel slope of FeP@NPC/NF-450 being 57.90 mV dec−1, significantly lower than those of FeP@NPC/NF-400 (72.81 mV dec−1), Mo-FeP@NPC/NF-500 (97.63 mV dec−1), Fe2O3@NC/NF (210.42 mV dec−1), and Ni foam (140.95 mV dec−1), indicating its superior catalytic kinetics during the HER process.
To evaluate the electron transfer dynamics of the synthesized catalysts, electrochemical impedance spectroscopy (EIS) measurements were performed. The charge transfer resistance (Rct) of the FeP@NPC/NF-450 catalyst was 3.85 Ω cm−2, lower than that of FeP@NPC/NF-400 (4.41 Ω cm−2), FeP@NPC/NF-500 (6.63 Ω cm−2), Fe2O3@NC/NF (24.24 Ω cm−2), and Ni foam (17.78 Ω cm−2), suggesting a faster electron transfer rate during hydrogen production. To further investigate the electrochemical double-layer capacitance (Cdl) of the catalysts, cyclic voltammetry (CV) curves were recorded at different scan rates. As shown in Figure 7d, the Cdl value of FeP@NPC/NF-450 was 11.68 mF cm−2, significantly higher than those of FeP@NPC/NF-400 (3.36 mF cm−2), FeP@NPC/NF-500 (2.47 mF cm−2), Fe2O3@NC/NF (0.72 mF cm−2), and Ni foam (1.49 mF cm−2), indicating a larger electrochemically active surface area and more available active sites for hydrogen production.
The synthesized FeP@NPC/NF-450 catalyst exhibits excellent stability in 0.5 M H2SO4, as shown in Figure 8. After 1000 cycles, the LSV curve shows almost no change. Simultaneously, after 48 h of chronoamperometry testing, the change in current density is negligible, demonstrating its remarkable catalytic stability.

3. Experimental Section

3.1. Chemicals

All chemicals were used as received without further purification. Hydrochloric acid was purchased from Shanghai Titan Technology Co., Ltd. Sodium hypophosphite (NaH2PO2) was obtained from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). 2-Methylimidazole (C4H6N2) was purchased from Adamas-beta (Shanghai, China) Chemical Reagent Co., Ltd. Ethanol (C2H5OH) was acquired from Jiangsu Qiangsheng Functional Chemical Co., Ltd. (Changshu, China) Iron(III) chloride (FeCl3) was purchased from Shanghai Runjie Chemical Reagent Co., Ltd. (Shanghai, China).

3.2. Pretreatment of Nickel Foam

First, the nickel foam was cut into small pieces of 40 mm × 25 mm. The cut nickel foam was immersed into 1 M HCl, deionized water, and anhydrous ethanol to ultrasonicate for 20 min. After the ultrasonication, a hair dryer was used to blow dry the pieces for spare.

3.3. Preparation of Fe-MOF Precursor on Nickel Foam

Firstly, 2 mmol of FeCl3 was added to 50 mL of deionized water and stirred until completely dissolved. Then, 10 mmol of 2-methylimidazole was added, and the mixture was stirred for an additional 30 min to obtain the Fe-MOF precursor [18]. The pretreated nickel foam was then immersed in the Fe-MOF precursor solution and left to stand for 24 h. After 24 h, the nickel foam was removed and gently rinsed with deionized water and anhydrous ethanol to remove impurities and organic residues. Finally, the nickel foam was dried in an oven at 60 °C to obtain the Fe-MOF/NF precursor.

3.4. Preparation of FeP@NPC/NF

FeCl3 was dissolved in the DI water to form uniform Fe2+ solution. 2-methylimidazole was dissolved in the FeCl3 solution to prepared Fe-MOF precursor. Ni foam was soaked in the above-mentioned precursor to prepare Fe-MOF/NF precursor. Then, the prepared precursor was transferred to FeP@NPC/NF under phosphorization reaction.
The FeP@NPC/NF samples were prepared using a high-temperature phosphorization method under argon protection. The Fe-MOF/NF precursor and 0.4 g of sodium hypophosphite were placed separately at the downstream and upstream positions of a porcelain boat, respectively. The porcelain boat was then transferred to a tube furnace. Before heating, the tube furnace was evacuated and purged with argon gas three times. Under an argon atmosphere, the furnace was heated at 2 °C/min to 450 °C and maintained at this temperature for 2 h. The furnace was then cooled at a rate of 5 °C/min to 200 °C, followed by natural cooling to room temperature to obtain the phosphorized FeP@NPC/NF catalyst at 450 °C, designated as FeP@NPC/NF-450. For comparison, the phosphorization of Fe-MOF/NF was conducted at 400 °C and 500 °C under otherwise identical conditions, resulting in FeP@NPC/NF-400 and FeP@NPC/NF-500, respectively. Additionally, Fe-MOF/NF was thermally treated at 450 °C without adding a phosphorus source under the same conditions, yielding Fe2O3@NC/NF.

3.5. Preparation of FeP Powder Material Without Ni Foam

After Ni foam had been immersed for 24 h in the Fe-MOF precursor solution, powders were collected from the baker. The collected powder was washed and dried, then annealed under the same condition of FeP@NPC/NF, the prepared sample was labeled as FeP@NPC.

3.6. Material Characterization

The crystal structure of the prepared powder material (sample without Ni foam) was analyzed using powder X-ray diffraction (XRD, Rigaku SmartLab, Cambridge, MA, USA) with Cu Kα1 radiation (λ = 1.5406 Å) in the 2θ range of 20° to 80°. The microstructure was further investigated using scanning electron microscopy (FE-SEM, Hitachi SU8600, Tokyo, Japan). The surface chemical composition of the catalyst was determined by X-ray photoelectron spectroscopy (XPS, ThermoFisher Nexsa, Waltham, MA, USA).

3.7. Electrochemical Measurements

The HER performance was analyzed using a standard three-electrode system with a CHI 660E electrochemical workstation. The reference and counter electrodes were saturated calomel electrode (SCE) and a Pt sheet. The working area of the working electrode was 1 cm × 1 cm, and the HER was conducted in a 1 M KOH solution and 0.5 M H2SO4 solution. All electrode potentials (vs. SCE) were calibrated to a reversible hydrogen electrode (RHE) and IR-corrected (solution resistance), namely, E(RHE) = E(SCE) + 0.244 + (0.0599 × pH) − iRs (at 25 °C) [43,44]. The linear sweep voltammetry (LSV) rate was 3 mV s−1, and the electrochemical impedance spectroscopy (EIS) was analyzed at a voltage of 106.1 mV (1 M KOH) and 68.3 mV (0.5 M H2SO4) in the frequency range of 100 KHz to 10 MHz.
According to the formula given in [45],
ECSA = Cdl/Cs
The electrochemical active surface area (ECSA) can be analyzed through the double-layer capacitance (Cdl), and the Cdl of catalysts was evaluated based on the cyclic voltammogram (CV). The CV curves of the catalysts were tested at scan rates from 20 to 100 mV s−1. The slope of the fitted linear regression function (Δj = janodic − jcathodic) vs. scan rate) equals the value of Cdl.

4. Conclusions

In conclusion, we have devised a novel structure aimed at augmenting the activity and stability of FeP nanoparticles. A simple phosphidation method was employed to synthesize nitrogen and phosphorus co-doped carbon-coated FeP nanoparticles supported on nickel foam (FeP@NPC/NF). The N, P co-doped carbon serves to prevent the aggregation of FeP nanoparticles by encapsulating them, thereby increasing the number of active sites and shielding the FeP nanoparticles from corrosion and oxidation during the hydrogen production process. The multi-controllable network structure of the nickel foam offers a larger specific surface area during the hydrogen evolution reaction (HER) and facilitates gas release. The results demonstrate that FeP@NPC/NF-450 exhibits excellent HER activity in acidic and alkaline environments. In 1.0 M KOH and 0.5 M H2SO4, the hydrogen evolution overpotentials at a current density of 10 mA cm−2 were 68.3 mV and 106.1 mV, respectively, with corresponding Tafel slopes of 57.90 mV dec−1 and 110.73 mV dec−1. Moreover, it showed long-term stability for 48 h in both acidic and alkaline media, surpassing the performance of recently reported FeP-based HER catalysts. This study provides a simple approach for improving the activity and stability of FeP-based electrocatalysts, presenting a promising application in green energy conversion, where highly active HER catalysts are essential.

Author Contributions

J.Z.: Investigation, Data curation, Writing—original draft. T.Z.: Methodology, Formal Analysis, Supervision. J.T.: Formal Analysis W.G.: Writing—review and editing. Y.W.: Supervision. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by [Jiangsu Province Natural Science Foundation for Youths] grant number [No. BK20241021].

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors would like to acknowledge the assistance of the staff at the Jiangsu University of Science and Technology. Ting Zhang was supported by the “Jiangsu Province Excellent Postdoctoral Program”.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Inorganics 12 00291 g001
Figure 1. The XRD patterns of FeP@NPC/NF samples subjected to heat treatment at 400 °C, 450 °C, and 500 °C, along with the Fe2O3@NC/NF sample heat−treated at 450 °C.
Figure 1. The XRD patterns of FeP@NPC/NF samples subjected to heat treatment at 400 °C, 450 °C, and 500 °C, along with the Fe2O3@NC/NF sample heat−treated at 450 °C.
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Figure 2. SEM images of FeP@NPC/NF−400 (a–c), FeP@NPC/NF−450 (d–f), and FeP@NPC/NF−500 (g−i) at different magnifications; elemental mapping images of FeP@NPC/NF−450 (j).
Figure 2. SEM images of FeP@NPC/NF−400 (a–c), FeP@NPC/NF−450 (d–f), and FeP@NPC/NF−500 (g−i) at different magnifications; elemental mapping images of FeP@NPC/NF−450 (j).
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Figure 3. TEM images of (a) FeP@NPC/NF−450 and (b) high-resolution TEM of FeP@NPC/NF−450.
Figure 3. TEM images of (a) FeP@NPC/NF−450 and (b) high-resolution TEM of FeP@NPC/NF−450.
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Figure 4. (a) FeP@NPC/NF−450 XPS survey spectrum; high-resolution XPS spectrum of FeP@NPC/NF−450: (b) Ni 2p, (c) Fe 2p, (d) P 2p, (e) N 1s, (f) C 1s.
Figure 4. (a) FeP@NPC/NF−450 XPS survey spectrum; high-resolution XPS spectrum of FeP@NPC/NF−450: (b) Ni 2p, (c) Fe 2p, (d) P 2p, (e) N 1s, (f) C 1s.
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Figure 5. Electrochemical tests of catalysts in 1 M KOH: (a) LSV curve and (b) Tafel slope of FeP@NPC/NF−400, FeP@NPC/NF−450, FeP@NPC/NF−500, Fe2O3@NC/NF, Ni foam, and Pt sheet; (c) Nyquist plot and (d) capacitive current difference versus scan rate of FeP@NPC/NF−400, FeP@NPC/NF−450, FeP@NPC/NF−500, Fe2O3@NC/NF, and Ni foam.
Figure 5. Electrochemical tests of catalysts in 1 M KOH: (a) LSV curve and (b) Tafel slope of FeP@NPC/NF−400, FeP@NPC/NF−450, FeP@NPC/NF−500, Fe2O3@NC/NF, Ni foam, and Pt sheet; (c) Nyquist plot and (d) capacitive current difference versus scan rate of FeP@NPC/NF−400, FeP@NPC/NF−450, FeP@NPC/NF−500, Fe2O3@NC/NF, and Ni foam.
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Figure 6. (a) Stability of FeP@NPC/NF−450 before and after 1000 cycles, and (b) chronoamperometric curve of FeP@NPC/NF−450 at 106.1 mV for 48 h in 1.0 M KOH.
Figure 6. (a) Stability of FeP@NPC/NF−450 before and after 1000 cycles, and (b) chronoamperometric curve of FeP@NPC/NF−450 at 106.1 mV for 48 h in 1.0 M KOH.
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Figure 7. Electrochemical tests of catalysts in 0.5 M H2SO4: (a) LSV curves of FeP@NPC/NF-400, FeP@NPC/NF−450, FeP@NPC/NF−500, Fe2O3@NC/NF, nickel foam, and Pt sheet; (b) Tafel slopes; (c) Nyquist plots of FeP@NPC/NF−400, FeP@NPC/NF−450, FeP@NPC/NF−500, Fe2O3@NC/NF, and nickel foam; (d) capacitive current difference versus scan rate.
Figure 7. Electrochemical tests of catalysts in 0.5 M H2SO4: (a) LSV curves of FeP@NPC/NF-400, FeP@NPC/NF−450, FeP@NPC/NF−500, Fe2O3@NC/NF, nickel foam, and Pt sheet; (b) Tafel slopes; (c) Nyquist plots of FeP@NPC/NF−400, FeP@NPC/NF−450, FeP@NPC/NF−500, Fe2O3@NC/NF, and nickel foam; (d) capacitive current difference versus scan rate.
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Figure 8. (a) Stability of FeP@NPC/NF−450 before and after 1000 cycles, and (b) chronoamperometric curve of FeP@NPC/NF−450 at 68.3 mV for 48 h in 0.5 M H2SO4.
Figure 8. (a) Stability of FeP@NPC/NF−450 before and after 1000 cycles, and (b) chronoamperometric curve of FeP@NPC/NF−450 at 68.3 mV for 48 h in 0.5 M H2SO4.
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MDPI and ACS Style

Zhong, J.; Zhang, T.; Tian, J.; Gao, W.; Wang, Y. Nickel Foam-Supported FeP Encapsulated in N, P Co-Doped Carbon Matrix for Efficient Electrocatalytic Hydrogen Evolution. Inorganics 2024, 12, 291. https://doi.org/10.3390/inorganics12110291

AMA Style

Zhong J, Zhang T, Tian J, Gao W, Wang Y. Nickel Foam-Supported FeP Encapsulated in N, P Co-Doped Carbon Matrix for Efficient Electrocatalytic Hydrogen Evolution. Inorganics. 2024; 12(11):291. https://doi.org/10.3390/inorganics12110291

Chicago/Turabian Style

Zhong, Jianguo, Ting Zhang, Jianqiang Tian, Wei Gao, and Yuxin Wang. 2024. "Nickel Foam-Supported FeP Encapsulated in N, P Co-Doped Carbon Matrix for Efficient Electrocatalytic Hydrogen Evolution" Inorganics 12, no. 11: 291. https://doi.org/10.3390/inorganics12110291

APA Style

Zhong, J., Zhang, T., Tian, J., Gao, W., & Wang, Y. (2024). Nickel Foam-Supported FeP Encapsulated in N, P Co-Doped Carbon Matrix for Efficient Electrocatalytic Hydrogen Evolution. Inorganics, 12(11), 291. https://doi.org/10.3390/inorganics12110291

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