Flexible electrospun Co–Cu/PVDF-HFP catalysts for hydrogen generation from NaBH₄ methanolysis

2.1. Materials and reagents

Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP; Mw = 65,000 g/mol), cobalt acetate tetrahydrate (CoAc, ≥98%), copper acetate monohydrate (CuAc, ≥99%), N,N-dimethylformamide (DMF, ≥99.8%), methanol (MeOH, ≥99.8%), and sodium borohydride (NaBH₄ / SBH, ≥98%) were procured from Sigma Aldrich. All reagents were used as obtained, without further purification. Deionized water (DW) was utilized consistently throughout the investigation.

2.2. Synthesis of Co-Cu@PVDF-HFP catalyst

A series of Co–Cu nanocatalysts supported on PVHF nanofibers with different Co:Cu ratios (x = 0, 10, 20, 40, 60, 80, 100) were synthesized. First, a 15 wt% PVDF-HFP solution was prepared by dissolving PVHF powder in a mixture of DMF and acetone with a ratio of 4:1 under continuous magnetic stirring overnight to ensure complete dissolution. In a separate vessel, stoichiometric amounts of CoAc and CuAc corresponding to the desired molar ratios were dissolved in 5 mL of DMF and stirred for 30 minutes to obtain a homogeneous metal precursor solution. This solution was then slowly added to the PVHF solution with continuous stirring for 5 hours to form a homogeneous sol-gel. The resulting sol-gel was electrospun using a lab-scale electrospinning machine at an applied voltage of 15 kV, a flow rate of 0.6 mL/h through a 20 mL syringe, and a tip-to-collector distance of 15 cm. The collector was a grounded rotating stainless steel drum operating at 150 rpm, covered by an aluminum sheet. The ambient temperature during electrospinning was 25 ± 2°C, and the relative humidity was maintained at 40 ± 5%. The as-spun NF mats were peeled off from the aluminum foil and vacuum-dried at 40°C overnight to remove residual solvent. The synthesized catalysts were denoted based on the Co:Cu ratio in the PVDF-HFP support. The series included PVHF-0Co (Co:Cu ratio = 0:100), PVHF-10Co (10:90), PVHF-20Co (20:80), PVHF-40Co (40:60), PVHF-60Co (60:40), PVHF-80Co (80:20), and PVHF-100Co (100:0).

2.3. Chemical reduction of CoCu@PVHF nanofibrous membranes

The electrospun nanofiber mats were immersed in a methanolic solution of SBH at an SBH : metal precursor molar ratio of 5:1 to ensure complete reduction of both Co²⁺ and Cu²⁺. Upon immersion, the membrane color progressively changed to deep black, indicating the reduction of metal ions, while vigorous bubbling of H₂ gas was observed on the fiber surface. The reaction was allowed to continue until gas evolution ceased, signifying complete reduction. The reduced membranes were then rinsed repeatedly with deionized water and ethanol to remove residual borates or by-products and vacuum-dried at 30°C overnight.

2.4. Characterization of prepared membranes

The physicochemical characterizations of the synthesized membranes were conducted using identical techniques as in our recent publications (Al-Enizi et al., 2022). The porosity (P) of the prepared NF membranes was determined by immersing the dried samples in n-butanol (BuOH) for 1 h. P was calculated using the following equation (Raghavan et al., 2008):

Where M_m is the mass of the dry membrane, M_BuOH is the mass of absorbed n-butanol, ρ_BuOH is the density of n-butanol, and ρ_p is the PVHF density.

2.5. Evaluation of catalytic activity of Co-Cu@PVDF-HFP for H₂ generation via SBH methanolysis

The catalytic performance of the synthesized Co-Cu@PVDF-HFP nanocomposite was systematically investigated for H₂ production through the methanolysis of SBH under well-controlled experimental conditions. In each experiment, 100 mg of the catalyst was dispersed in 20 mL of methanol under continuous magnetic stirring at ambient temperature. A 1 mM solution of SBH was subsequently introduced into a round-bottom reaction flask placed atop a magnetic stirrer. The generated hydrogen gas was quantified using a water displacement setup, where an inverted, water-filled graduated cylinder was employed to collect the displaced volume of H₂. To ensure measurement accuracy and prevent gas leakage, the reaction was performed in a hermetically sealed glass reactor, which facilitated the precise collection of evolved hydrogen through the displacement method. The progression of the reaction was monitored over time, and the cumulative hydrogen volume was recorded at predefined intervals. A comprehensive evaluation of the catalyst’s efficiency involved studying three principal reaction variables: catalyst dosage, SBH concentration, and reaction temperature. Catalyst loading was varied from 100 mg to 250 mg to assess its influence on hydrogen evolution, while the SBH concentration was systematically modified in the 1–4 mM range to determine the effect of reactant availability on hydrogen yield. Additionally, the temperature dependence of the reaction kinetics was examined by conducting the experiments at 30 °C, 35 °C, 40 °C, and 45 °C. The corresponding data were used to calculate the apparent activation energy (Ea) through Arrhenius analysis. To evaluate the catalyst’s durability and reusability, recycling experiments were performed. After each cycle, the used catalyst was recovered without any intermediate washing or treatment and reused under identical reaction conditions. This procedure allowed for an accurate assessment of the catalyst’s structural stability and long-term functional performance over successive cycles.

3.1. Characterization of hybrid nanofiber mats

The fabrication of polymeric NF membranes via electrospinning offers several structural and functional advantages, including high porosity, interconnected architecture, enhanced flexibility, and a large surface-to-volume ratio of the membranes (Gibson et al., 2001, Yousef et al., 2012). These properties make electrospun membranes excellent platforms for catalytic applications. PVDF-HFP, in particular, is widely preferred as a base polymer due to its semi-crystalline structure, notable thermal resistance, hydrophobicity, and electroactive properties such as piezoelectricity and pyroelectricity (Shin et al., 2010, Kumar 2011), which contribute to its stability during processing. SEM images of the electrospun PVHF-100Co and PVHF-0Co membranes (Fig. 1a and b) reveal uniform, bead-free NFs with well-developed porous networks. Such porosity is attributed to the rapid evaporation of volatile solvents—especially acetone—during the electrospinning process as the jet transitions from the high-voltage syringe tip to the grounded collector. This rapid phase separation leads to the formation of nanoscale pores, which serve as favorable sites for the deposition of metal NPs. When Co and Cu acetate salts are incorporated into the PVDF-HFP solution, their hydration content facilitates phase demixing during fiber formation. This enhances pore development on the fiber surface due to the hydrophobic nature of the polymer, promoting more effective exposure of active sites. Consequently, this structure enables efficient entrapment of reactants while minimizing mass transfer limitations, thus enhancing catalytic performance, particularly in H₂ generation reactions. SEM images of electrospun PVHF-10Co, PVHF-20Co, PVHF-40Co, PVHF-60Co, and PVHF-80Co (Figs. 1c-g) show rough, interconnected NFs without beads, confirming the successful formation of a continuous fibrous network. The structures of these membranes enable homogeneous distribution of reduced Co and Cu NPs across the fiber surfaces. Adding metal salts to the precursor solution made the electrospinning jet more electrically conductive and viscous. This improved the elongation dynamics and resulted in more uniform fiber morphologies. The PVHF-100Co nanofibers had an average fiber diameter of 134.56 nm (Fig. 2a), whereas the PVHF-0Co nanofibers had a lower diameter of 93.31 nm (Fig. 2b). When Cu was added to the system, the fiber diameter noticeably decreased. The average diameters were 77.39 nm for PVHF-10Co (Fig. 2c), 84.45 nm for PVHF-20Co (Fig. 2d), 88.52 nm for PVHF-40Co (Fig. 2e), 90.92 nm for PVHF-60Co (Fig. 2f), and 101.54 nm for PVHF-80Co (Fig. 2g). The obtained data show that adding Cu reduced the fiber size. This could be due to changes in the solution characteristics that enhance jet stretching during electrospinning. Elemental mapping (Figs 3a–f) confirms the even distribution of Co and Cu throughout the PVHF-60Co membrane matrix, supporting the observations from SEM analysis. The as-electrospun Co–Cu precursor/PVHF NF membranes exhibited visibly colored surfaces, reflecting the incorporation of the metal precursors into the polymer matrix. Upon chemical reduction of the immobilized metal ions, the membranes underwent a pronounced color change to deep black, consistent with the in situ formation of metallic NPs within the polymer network. TEM images of PVHF-60Co (Fig. 4) confirmed this transformation. The PVHF-60Co NF membranes display a dense dispersion of dark, high-contrast NPs embedded on and within the NF walls (Fig. 4a and b). The darker contrast of these domains reflects the higher electron density of the metallic Co–Cu species relative to the surrounding polymer. This microstructural evidence confirms that the reduction process not only converts the precursor salts to their metallic states but also drives the nucleation and growth of well-distributed nanoparticles throughout the PVHF NF network, producing a hybrid structure with an enlarged interfacial area and potentially enhanced catalytic activity.

Close

Fig. 1.

SEM images of (a) PVHF-100Co, (b) PVHF-0Co, (c) PVHF-10Co, (d) PVHF-20Co, (e) PVHF-40Co, (f) PVHF-60Co, and (g) PVHF-80Co.

Export to PPT

Close

Fig. 2.

Size distribution of (a) PVHF-100Co, (b) PVHF-0Co, (c) PVHF-10Co, (d) PVHF-20Co, (e) PVHF-40Co, (f) PVHF-60Co, and (g) PVHF-80Co.

Export to PPT

Close

Fig. 3.

(a) SEM image (b) mapping showing the spread of elements, (c) Carbon, (d) fluorine, (e) cobalt, and (f) copper in the PVHF-60Co NFs.

Export to PPT

Close

Fig. 4.

(a-b) TEM images of the PVHF-60Co NF membrane.

Export to PPT

EDX spectroscopy (Figs. 5a and 3b) further validates the incorporation of Co, Cu, C, and F elements (Figs. 5a and 5b). The results demonstrate the effectiveness of the electrospinning process in producing structurally stable, catalytically active membranes with well-integrated bimetallic NPs. Fig. 6 presents the XRD patterns of the as-spun PVHF-60Co NF membranes. The diffraction peaks observed at 2θ values of around 18.2°, 20.0°, and 26.6° correspond to the (100), (020), and (110) planes of the semi-crystalline PVDF-HFP matrix (Stephan et al., 2006). No characteristic peaks were detected in the patterns for Co or Cu phases, indicating the absence of long-range crystalline order for the metallic species. This can be attributed to the amorphous nature of the Co and Cu NPs, which likely developed during the chemical reduction of metal precursors with SBH. The rapid nucleation and growth kinetics associated with this reduction process typically favor the formation of non-crystalline metallic domains, especially when dispersed within a polymeric matrix.

Close

Fig. 5.

(a) SEM image (b) mapping showing the spread of elements, (c) carbon, (d) fluorine, (e) cobalt, and (f) copper in the PVHF-60Co NFs.

Export to PPT

Close

Fig. 6.

XRD of PVHF-60Co NFs membrane.

Export to PPT

XPS was utilized to elucidate the surface electronic states and chemical composition of the synthesized catalysts. The full-scan spectrum of the PVHF-60Co NF membrane reveals well-defined photoelectron lines at binding energies of 530.09, 286.94, and 690.49 eV, which are assigned to the O 1s, C 1s, and F 1s core levels, respectively (Fig. 7a). The detection of oxygen is generally unavoidable and can be attributed to surface oxidation during exposure of the membrane to air and sample preparation for XPS analysis (Zhou et al., 2018, Zouli et al., 2023). The high-resolution spectra provide further insight into the oxidation states of Co and Cu species embedded in the polymer matrix. As shown in Fig. 7(b), the Co 2p region exhibits intense components at 797.23 eV (Co 2p1/2) and 781.04 eV (Co 2p3/2). Additional peaks at 807.19 and 783.48 eV are characteristic of Co²⁺ species, while signals at 797.39 and 780.85 eV can be attributed to Co³⁺ centers. The presence of satellite features at 805.80 and 789.68 eV further supports the assignment of Co²⁺, whereas satellites at 803.52 and 786.37 eV are indicative of Co³⁺ species. These findings collectively confirm that Co exists in mixed valence states, consistent with previous reports (Lu et al., 2023, Yuan et al., 2024). Similarly, the Cu 2p spectra (Fig. 7c) display two principal photoelectron peaks at approximately 934.62 and 954.31 eV corresponding to Cu²⁺. Several satellite peaks at 938.48, 941.66, 944.00, and 961.97 eV appear at higher binding energies, which are characteristic of the incompletely filled Cu 3d⁹ shell of Cu⁺ species; this is in agreement with previous literature (Yuan et al., 2020). Table 1 reveals that all of the membranes had high porosity (>70%), which suggests that electrospinning is an effective method to make porous nanofibers. The pristine PVHF had the most porosity (84.5%). Adding metal made the porosity a little lower because it changed how the jets moved and how the fibers were packed. The specimens PVHF-100Co kept their porosity near to that of the blank, but membranes rich in Cu exhibited bigger drops, which means that Cu has a higher densifying impact. Even though this decrease happened, all of the membranes still had high enough porosity to allow for effective mass transfer and easy access to catalytic sites, which is good for producing H₂.

Close

Fig. 7.

XPS spectra of the PVHF-60Co NFs membrane: (a) full spectrum, (b) Co2p, and (c) Cu2p

Export to PPT

3.2. Hydrogen generation from SBH

A series of Co–Cu@PVDF-HFP catalysts with varying Co:Cu ratios were fabricated via electrospinning followed by in situ chemical reduction. Each catalyst formulation (100 mg) was evaluated for H₂ generation through the methanolysis of SBH under identical conditions: 1 mM SBH, 30°C, and 1000 rpm. The H₂ evolution profiles, presented in Fig. 8(a), reveal substantial differences in activity depending on the metal composition. The control experiment without catalyst, which lacks both Co and Cu, exhibited minimal activity, producing only 72 and 63 mL of hydrogen over 30 minutes respectively. Furthermore, the catalytic performance of PVHF-0Co in SBH methanolysis was much poorer compared with all formulated catalysts. Meanwhile, Co-containing catalysts significantly accelerated hydrogen release. Within just 15 minutes, catalysts with varying Co content produced the following hydrogen volumes: 62 mL (PVHF-10Co), 65 mL (PVHF-20Co), 76 mL (PVHF-40Co), 82 mL (PVHF-60Co), and 80 mL (PVHF-80Co). Notably, PVHF-60Co demonstrated the highest catalytic efficiency, representing the optimal Co:Cu ratio for SBH methanolysis. The catalytic activity trend highlights the importance of Co as the principal active component for SBH methanolysis, consistent with the prior finding that Co exhibits higher intrinsic activity than Cu in H₂ release from SBH (Fig. 8b). The Co–Cu bimetallic catalysts consistently outperformed their monometallic counterparts, underscoring the synergistic interplay between Co and Cu atoms. This synergy is attributed to both electronic effects arising from differences in electronegativity and geometric effects due to alloy formation (Li et al., 2015). The PVHF support structure also plays a crucial role in catalyst efficiency. Its electrospun nanofibrous architecture provides a high surface area and interconnected pore network, promoting efficient diffusion of SBH to active sites and enhancing H₂ desorption. Additionally, the hydrophobic and chemically stable nature of PVHF ensures uniform dispersion of metal NPs and long-term catalyst stability. The enhanced performance of the Co–Cu systems aligns with previous reports demonstrating that bimetallic catalysts exhibit higher activity than their monometallic counterparts. In particular, the formation of CoCu alloy NPs facilitates electron transfer, modifies the d-band center of Co, and enhances adsorption/desorption kinetics. Such alloying effects are especially significant when the constituent metals have similar electronegativities, such as Co (1.88) and Cu (1.90), facilitating both electron mobility and lattice compatibility (Chou et al., 2015, Duan et al., 2016, Şahin et al., 2016, Didehban et al., 2018, Al-Thabaiti et al., 2019, Chairam et al., 2021). The formation of a byproduct, sodium tetramethoxyborate, partially deactivates the catalyst by forming a surface-passivating layer, accounting for the observed decline in H₂ evolution rate over time (Xu et al., 2012).

Close

Fig. 8.

(a-b) Cu–Co NPs@PVHF NFs influence the methanolysis of SBH. [The catalyst dose = 100 mg, [SBH] = 1mM, 1000 rpm and T = 30°C]

Export to PPT

The increased efficacy of Co-rich catalysts can be ascribed to synergistic interactions. The methanolysis of SBH utilizing Co–Cu catalysts occurs via a surface-mediated mechanism. The bimolecular Langmuir–Hinshelwood model is typically employed to elucidate the mechanisms of NaBH₄ hydrolysis in the presence of a catalyst (Dai et al., 2021, Saka 2022). Similarly, analogous fundamental procedures could be used for H₂ release from SBH methanolysis utilizing a CoCu@PVHF catalyst. Co ensembles act as the primary sites for B–H activation: BH₄– adsorbs on Co-rich domains and transfers a hydridic H– to Co, yielding surface Co–H species and a boron fragment (BH₃–) bound at the interface. The H atom acquires an electron from the Co, leading to the formation of the H– form; however, the BH₄– species remains bonded to the Co atom. Subsequently, the proton derived from methanol engages in a reaction with the hydridic H– ion, resulting in the formation of H₂. Concurrently, CH₃O– ions engage in a chemical reaction with boron in BH₃, resulting in the formation of BH₃(CH₃O)– ions. This procedure continues until the formation of four moles of H₂. Cu may serve as Lewis acid sites within the current catalyst framework. These sites are readily accessible for the absorption of Lewis bases such as CH₃O– ions. Consequently, the electron density on the active metal atoms increases, which enhances the kinetics of the reaction. Given its superior hydrogen production efficiency, the PVHF-60Co catalyst was selected for further kinetic and recyclability studies.

3.5. Factors affecting the catalytic activity of the catalyst

3.5.1. The effect of PVHF-60Co dosages

To investigate the influence of catalyst loading on the volume of generated H₂, a set of experiments were performed using various dosages (100, 150, 200, and 250 mg) of the PVHF-60Co nanofibrous catalyst membrane in the methanolysis of SBH, 1 mM at 30 °C. The evolution of H₂ over time is presented in Fig. 9(a): A pronounced enhancement in H₂ production is observed with increasing catalyst amount. Specifically, H₂ volumes of 51, 64, 76, and 82 mL were recorded for catalyst masses of 100, 150, 200, and 250 mg, respectively, at 6 minutes. This indicates that increasing the catalyst dosage significantly reduces the reaction time, from 15 minutes at lower dosages to 6 minutes at the highest dosage. This enhancement is attributed to the higher availability of active catalytic sites, facilitating faster methanolysis of SBH. The kinetic behavior, illustrated in Fig. 9(b), confirms a first-order dependence on catalyst concentration, as reflected by the linear relationship between ln(rate) and ln(catalyst dosage), with a slope of approximately 0.97 and an R² value of 0.99.

Close

Fig. 9.

(a) The effect of PVHF-60 Co on the methanolysis of SBH and (b) the log of the H₂ generation rate vs. log of catalyst dose. [[SBH] = 1mM, 1000 rpm, and T = 30°C]

Export to PPT

3.5.2. The effect of SBH

To explore the influence of SBH concentration on the catalytic methanolysis reaction, a series of experiments were performed using a constant catalyst dosage (100 mg of PVHF-60Co nanofibrous membrane) and methanol volume (20 mL) at a fixed temperature of 30 °C while varying SBH concentrations (1, 2, 3, and 4 mM). The corresponding H₂ evolution profiles are presented in Fig. 10(a). The results reveal a direct proportionality between the initial SBH concentration and the total H₂ volume produced. At 1 mM SBH, approximately 82 mL of H₂ was generated in 15 minutes, whereas 202 mL was evolved within 34 minutes at 4 mM SBH. Despite this increase in cumulative H₂ volume, the reaction rate remained nearly constant, as evidenced by the progressive increase in the time required to achieve similar H₂ volumes with increasing SBH concentrations. This trend indicates that the reaction rate is independent of SBH concentration, following apparent zero-order kinetics with respect to SBH, as confirmed by the linear plot of ln(rate) versus ln[SBH] shown in Fig. 10(b), with a slope of 0.18 and an R² value of 0.97. The observed zero-order behavior suggests that the reaction proceeds under conditions where the catalyst surface is saturated with SBH molecules, and the rate-determining step is not affected by further increases in SBH concentration. The high catalytic efficiency is due to the synergistic effect between Co and Cu species embedded in the PVHF membrane, enhancing the active site density and electronic conductivity—crucial factors in accelerating H₂ evolution. These results confirm that the PVHF-60Co catalyst demonstrates consistent and scalable performance under various SBH concentrations, emphasizing its potential for practical H₂ generation systems.

Close

Fig. 10.

The impact of SBH concentration on (a) hydrogen release and the (b) relationship between the log of hydrogen generation and the log of SBH concentration are presented. [The catalyst dose = 100 mg of PVHF-60Co NFs membrane, 1000 rpm, and T = 30°C]

Export to PPT

3.5.3. The effect of temperature

To investigate the thermal dependence of H₂ generation via catalytic methanolysis of SBH, a series of experiments were conducted at temperatures of 30 °C, 35 °C, 40 °C, and 45 °C using 20 mL of 1 mM SBH in methanol and 100 mg of the PVHF-60Co catalyst. The time-dependent H₂ evolution profiles are presented in Fig. 11(a), demonstrating a clear improvement in reaction kinetics with increasing temperature. The reaction completion times were significantly reduced from 15 minutes at 30 °C to just 3 minutes at 45 °C, with a corresponding rise in cumulative H₂ volume. This indicates that temperature serves as a key driver accelerating the methanolysis process. The increase in catalytic activity at high temperatures can be ascribed to increased molecular collisions, improved diffusion rates, and faster electron transfer processes at the catalyst surface. The bimetallic system embedded in the PVHF membrane—comprising Co and Cu—plays a pivotal role in influencing this behavior. Co acts as a primary active center for SBH methanolysis, while Cu improves the membrane’s electrical conductivity and facilitates electron mobility between active sites, enhancing H₂ evolution. Kinetic parameters were extracted using the Arrhenius equation, with the activation energy (E_a) calculated from the linear plot of ln k versus 1/T shown in Fig. 11(b). The slope of this plot yielded an E_a value of 42.26 kJ mol⁻¹, consistent with efficient surface-catalyzed reactions involving metal hydride intermediates. The obtained E_a value aligns with the values reported in the literature (Table 2). Further thermodynamic insights were obtained using transition state theory, as depicted in Fig. 11(b) and (c). The enthalpy change (ΔH) and entropy change (ΔS) were determined to be 39.65 kJ mol⁻¹ and 0.099 kJ mol⁻¹ K⁻¹, respectively. The ΔH and ΔS could be used to determine the ΔG using Eqs. (4) and (5).

(4)

$\ln k_D=\ln \frac{k_B}{h}+\frac{\Delta S}{R}-\frac{\Delta H}{RT}$

(5)

$\Delta G=\Delta H-T\Delta S$

Close

Fig. 11.

(a) The effect of thermal on the methanolysis of SBH, (b) the Ln K for H₂ versus 1/T, and (c) the Ln KD as a function of the inverse of the temperature versus 1/T. [The amount of catalyst = 100 mg of PVHF-60CoNFs membrane, [SBH] = 1mM, and 1000 rpm]

Export to PPT

Table 2. The reported Ea values of reported catalysts for methanolysis of SBH.

Catalyst	Ea (KJ·mol⁻1)	Ref.
Ru/Al₂O₃	51.0	(Su et al., 2012)
Ru–Co/C	36.83	(Wang et al., 2018)
NiB supporated on Spirulina microalgae	34.7	(Kaya 2019)
Metal-free catalyst	47.1	(Srivastava et al., 2023)
Ni₂P/SiO₂	45.0	(Yan et al., 2015)
Co–P/CNT–Ni foam	40.0	(Wang et al., 2018)
ZIF-67@graphene oxide	42.0	(Dai et al., 2021)
CoCu@PVDF–HFP nanofibers membrane	42.26	This study

The following is a concise summary of the ΔG equation:

The negative ΔG values at all tested temperatures confirm the spontaneous nature of the reaction. The moderate positive ΔH value suggests an endothermic character, while the positive ΔS value reflects increased disorder due to hydrogen gas release during the reaction. Overall, the strong temperature dependence, coupled with the low activation energy and favorable thermodynamic parameters, highlight the efficiency and practicality of using the PVHF-60Co catalyst in hydrogen generation systems. The synergistic interaction between Co and Cu within the polymer matrix provides greater active surface area and superior charge transfer characteristics, making this composite a promising candidate for scalable green hydrogen production technologies.

3.5.4. Reusability of the catalyst

Catalyst reusability, operational durability, and sustained activity are critical criteria for assessing the practicality of catalytic systems in H₂ production. To evaluate the cyclic performance of the PVHF-60Co catalyst, consecutive methanolysis reactions were performed under identical conditions. In the initial run, 20 mL of 1 mM SBH in methanol was reacted with 100 mg of the catalyst. For the subsequent cycles, only SBH was freshly replenished, while the same catalyst and reaction medium were retained. As illustrated in Fig. 12, the catalyst maintained full conversion efficiency across all cycles, confirming its robustness and high catalytic activity. However, a gradual decline in reaction rate was observed with successive uses, retaining 75% of activity after the seventh cycle. This behavior can be attributed to several intertwined factors: the progressive increase in solution viscosity, the rise in the basicity of the reaction medium, and partial surface deactivation of the catalyst, likely due to the accumulation of sodium methoxyborate byproducts on active sites. Despite the slight reduction in activity, the system consistently achieved complete hydrogen release, underscoring the structural and functional integrity of the PVHF-60Co catalyst. This stability under reuse conditions further reinforces the practical viability of a PVHF-60Co catalyst system for sustainable H₂ production. The catalyst’s performance affirms the advantage of bimetallic hybrid designs, as noted in previous temperature-dependent studies, where the cooperative behavior of Co and Cu led to improved catalytic efficiency, thermodynamic favorability, and kinetic acceleration. The XRD pattern after the reusability test (Fig. 13) reveals that the characteristic diffraction peaks of PVDF-HFP are largely preserved after repeated cycles, confirming that the polymeric scaffold maintains its semi-crystalline structure and overall integrity.

Close

Fig. 12.

Reusability test of PVHF-60Co catalyst [The catalyst dose= 100 mg of PVHF-60Co, [SBH] = 1mM, 1000 rpm and T = 30°C]

Export to PPT

Close

Fig. 13.

XRD after reusability test of PVHF-60Co catalyst

Export to PPT