Enhanced H2 production from dehydrogenation of sodium borohydride over the ternary Co0.97Pt0.03/CeOx nanocomposite grown on CGO catalytic support

The development of low-cost materials for the 100% dehydrogenation of metal hydrides is highly essential to vitalize the chemical hydride-based hydrogen economy. In this context, the ternary Co–Ce–Pt nanocomposite immobilized on functionalized catalytic support CGO is synthesized by the one step chemical reduction approach and has been directly employed for the ethanolysis of sodium borohydride. The co-operative effect of CGO and the synergy between metallic nanoparticles is investigated to determine the highest rate of hydrogen (H2) production. The maximum hydrogen generation rate (HGR) of 41.53 L (min gM)−1 is achieved with the Co0.97Pt0.03/CeOx/CGO nanohybrid from the alkaline ethanolysis of sodium borohydride (SB). In addition, the resultant nanohybrid exhibited a relatively low activation energy of 21.42 kJ mol−1 for the ethanolysis of SB. This enhanced catalytic activity may be attributed to the intermetallic charge transport among metallic Pt, Co/Co3O4, and CeOx counterparts. Moreover, the catalytic support CGO provides mesoporous functionalized surface and its intercalated GO layers promote charge transport. These results indicate that the resultant catalytic system described here for the dehydrogenation of SB can offer a portable and low-cost H2 supply for various fuel cell applications.


Introduction
"Hydrogen economy" is the most fascinating energy portfolio owing to its high energy density (142 MJ kg À1 ) and zero carbon emission, which can satisfy the current increasing demand for energy. However, its prociency for niche applications is mainly restricted due to inadequate molecular hydrogen (H 2 ) supply, its vital storage, and facile transport. 1 Nevertheless, various H 2 production routes are available but the dehydrogenation of chemical hydrides is the most attractive option to realize the high volume of H 2 production. 2 Among chemical hydrides, sodium borohydride (SB) is commended as the most promising candidate for H 2 supply owing to its high metal hydrogen storage capacity (10.8 wt%), low operating temperature, and hydrogen purity. 3 In general, H 2 production from SB proceeds via catalyzed hydrolysis reactions, according to eqn (1).
The hydrolysis byproduct, i.e., NaBO 2 , exhibits very low solubility in an aqueous medium, which usually causes the plugging problem in the reactor and its excess accumulation can deteriorate the active catalytic sites. Therefore, primary alcohols are proposed as alternative solvotic agents. 4,5 In particular, ethanol, with its low toxicity and production dependency on natural bio-resources, is an environmentally benign solvotic agent. 6,7 Moreover, ethanolic dehydrogenation reactions (eqn (2)) can be operated at sub-zero temperatures and most importantly, their by-products are easy to convert back to their parental form. 8 99.99%] were procured from Sigma-Aldrich. Graphite powder was obtained from the nano-shell. The synthesis of carbon nanoparticles (CNP) has been described in our previous article. 45 All the chemicals were used as obtained without further purication. Ordinary distilled water was used for synthesis and evaluation studies.

Synthesis of carbon-graed graphene oxide (CGO)
The catalytic support CGO was synthesized by the chemical oxidation of carbon nanoparticles (CNP) and graphitic powder by modied Hummers' method with a slight modication in the purication step. 44 In a typical synthesis, 2 g of CNP and 1 g of graphite powder were mixed mechanically and dispersed in (9 : 1) volume ratio of H 2 SO 4 and H 3 PO 4 in 1 L of ask. Then, 18 g of KMnO 4 was slowly added to the acid mixture with continuous stirring in the temperature range of 40-45 C. Aer continuous stirring for 30 min, the resultant mixture was reuxed for 12 h at 70 C. On the completion of oxidative treatment, the reaction was quenched by the addition of 400 mL of ice water along with 5-6 drops of 30% H 2 O 2 . The resultant solution was allowed to settle overnight; the slurry was centrifuged to obtain the sedimented product. The resultant composite was repeatedly washed with acetone-water mixture until the pH was neutral. The composite was dried at 60 C under vacuum.

Synthesis of
M ¼ weight of Co, Ce and Pt components in nanocomposite suspension is placed in a water bath at 27 AE 2 C and connected to a water-lled inverted measuring cylinder. The catalytic activity of the nanohybrid for the ethanolysis of SB was estimated in terms of HGR, as calculated by eqn (3). The reusability test of the nanohybrid has been performed by consecutively injecting 13.21 mM of alkaline SB aer each successive cycle in the same reaction mixture under similar experimental conditions. The recyclability experiment was performed by reusing the catalyst aer washing before the next run.

Catalyst characterization
Powder X-ray diffraction pattern (XRD) of the synthesized nanohybrid has been analyzed with a Rigaku Miniex-II diffractometer using Cu Ka 1 radiation at 30 kV and 15 mA with a monochromator. The diffraction pattern was recorded between 6 and 80 with a scanning speed of 3 min À1 . The X-ray diffractograms were compared with a standard JCPDS card. The surface morphology of the nanohybrid and the arrangement of NPs at the atomic scale was examined using a transmission electron microscope (TEM) (FEI, Tecnai T-20) operated at 200 kV. A high angle annular dark eld (HADDF) detector was used for the scanning transmission electron microscopic (STEM) experiment. The FT-IR of the prepared catalysts was recorded with the Bruker Model -152 Vertex-70 spectrophotometer using the KBr pellet technique. Raman measurements were obtained from a Renishaw Raman spectrophotometer. The Brunauer-Emmett-Teller (BET) specic surface area and Barrett-Joyner-Halenda (BJH) pore size distribution was evaluated using a Quantachrome Nova Touch NT1.1 surface area and a pore size analyzer, respectively. The samples were degassed at 200 C for 2 h to eliminate the physically adsorbed water and the atmospheric impurities prior to adsorption-desorption isotherm measurements. The samples for electron microscopy were prepared by dispersing the powder in ethanol and coating a very dilute suspension on carbon-coated Cu grids. Scanning Electron Microscopy (SEM) images and local elemental composition were determined using an FEI QUANTA 200 microscope and coupled with an energy dispersive X-ray analysis (EDX). The electronic structure of the synthesized bimetallic nanohybrid was investigated using high-resolution X-ray photoelectron spectroscopy (XPS). The measurement was performed using a VG Microtech Multilab ESCA 3000 spectrometer with a nonmonochromatized Mg Ka X-ray radiation. All the binding energies (BEs) were normalized using the adventitious carbon (C 1s ¼ 284.4 eV) as a reference. For further analysis, the peaks were deconvoluted by Voigt function.

Synthesis and characterization of the sample
In a typical synthesis, the ternary nanocomposite with different metallic molar ratio of Co, Ce, and Pt was grown on the CGO support by the facile chemical reduction approach using NaBH 4 as a reducing agent in an alkaline (12 wt% NaOH) ethanolwater medium at 300 K. The synthesis of CGO and ternary CoPt/ CeO x /CGO nanocomposite is represented in Fig. 1. Among the salts in the mixture, the Ce(III) ions are more susceptible to hydroxylation while the Co(II) and Pt(IV) ions can be deposited in their metallic state. On the addition of alkaline NaBH 4 solution, the generated black colored solution represented that the Pt(IV) and Co(II) ions could get reduced to their metallic state. The released heat during the course of reduction and dissolved oxygen of the solution could convert the Ce(III) hydroxylates into the amorphous CeO x oxide phase. In an alkaline environment, it may possible that some of the metallic cobalt may transform into the hydroxylate and with the aid of generated heat and could form the Co x O y oxide. 25,46 The instantaneously generated stream of H 2 largely inuences the crystallinity of the reduced metallic nanoparticles. In addition, it may facilitate the reduction of oxidized Co x O y to its metallic state. Therefore, it can be inferred that the in situ generated metallic Co, Pt, and amorphous CeO x nanoparticles served as the seeds for the successive growth of the ternary CoPt/CeO x nanocomposite on the CGO support. The resultant CoPt/CeO x /CGO nanohybrid has been tested for alkaline ethanolysis of SB at 300 K. Among all the tested metallic variations, the Co 0.97 Pt 0.03 /CeO x /CGO nanohybrid have shown the highest catalytic activity for dehydrogenation; therefore, it was used as a reference catalyst for instrumental characterization. The synthetic recipe and chemical composition of the Co, Ce, and Pt  Table 1.
The powder XRD pattern of CNP, GO, CGO, and Co 0.97 Pt 0.03 / CeO x are illustrated in Fig. 2(a) and (b). It was observed that the synthesized CGO exhibited both the characteristics of GO and CNP. The intense peak at about 10.74 represents the existence of graphene oxide, which originates from the reection of the (001) plane, while a broad peak at 24.8 belongs to the diffraction pattern of amorphous carbon. 39,47 Using Bragg's law, the interlayer spacing of GO and CGO for the (001) plane was calculated as 10.19 A and 9.47 A, respectively. Compared to GO, the observed slight shi in the peak position of CGO and the decreased d (001) value indicates the co-intercalation of amorphous carbon, nitrate, and sulfate in the graphitic layer during extensive chemical oxidation. 48 For Co 0.97 Pt 0.03 /CeO x /CGO, a very weak XRD signal was observed, which indicates the formation of ultrane nanoparticles occurring during the onestep reduction process or their embedment under CGO layers. XRD measurement without the support, i.e., Co 0.97 Pt 0.03 /CeO x , showed the dominant diffraction pattern of Co 3 O 4 [JCPDS # 74-2120], 49 while the presence of metallic Co, Pt, and CeO x counterparts remains undetected, probably due to the low resolution of the instrument. Further, the surface functional groups of CGO and its degree of graphitization were evaluated using Fourier transform infrared (FT-IR) and Raman spectroscopic technique, respectively.
The relative FT-IR spectrum of CNP and CGO is described in Fig. S1. † The IR stretching frequencies at 1720 cm À1 , 1590 cm À1 , 1250 cm À1 , and 870 cm À1 represent the symmetric vibration of C]O, C]C, C-O, and C-OH bonds, respectively. 44,47 These obtained functionalities may allow the homogenous distribution of metallic nanoparticles. The Raman spectrum of CNP, CGO, and Co 0.97 Pt 0.03 /CeO x /CGO are shown in Fig. S2. † In CGO, the distinct D and G band situated at 1346 cm À1 and 1584 cm À1 conrmed the formation of the graphene oxide phase. 41,42 The increased intensity ratio of the D and G band in Co 0.97 Pt 0.03 /CeO x /CGO (I D /I G ¼ 1.19) compared to CGO (I D /I G ¼ 1.06) could suggest the formation of more sp 2 hybridized domain on NaBH 4 reduction. 50 The alliance of the increased graphene domain may promote the intermetallic charge transport among the metallic counterparts. 27,47 The specic surface area and pore size of the as-prepared catalyst was studied by N 2 -adsorption analysis. The Brunauer-Emmett-Teller (BET) specic surface areas of CGO and Co 0.97 Pt 0.03 /CeO x / CGO were 37.12 and 30.16 m 2 g À1 , respectively. Compared to the support, the lower surface area of the composite is due to the blocking of the CGO pores by metal NPs during preparation. As shown in Fig. 3(a), the N 2 adsorption-desorption isotherm of CGO and Co 0.97 Pt 0.03 /CeO x /CGO reected type-IV isotherms with a hysteresis loop observed within the relative pressure range of 0.7-0.9. The pore size distribution in CGO and Co 0.97 Pt 0.03 /CeO x /CGO [ Fig. 3(b)] was analyzed with the Barrett-Joyner-Halenda (BJH) technique, which shows the maxima in the mesoporous region with an average pore size of 1.06, which corroborates the mesoporous nature of CGO and the trimetallic nanohybrid.
The microstructure of the synthesized CGO was examined by Transmission Electron Microscopy (TEM). The low-resolution TEM image [ Fig. 4(a)] shows that the CGO particles are fused together in a chain-type structure with irregularity at the edges. These irregularities may appear due to extensive chemical oxidation. The HR-TEM image shown in Fig. 4(b) represents the    52 can be assigned to Co 3 O 4 (311) and the metallic Pt NPs, respectively. Compared to the JCPDS database, the observed downshi value in the d-spacing of Pt nanoparticles could suggest the dominant interaction among the Pt, Co, and CeO x counterparts. 53 The corresponding SAED pattern [ Fig. 4(h)] showed that Co x O y has a higher degree of crystallinity compared to other metallic components. The d-spacing value of 0.240 nm calculated from the SAED pattern conrmed the presence of crystalline Co 3 O 4 (311). Regardless of the co-existence of cobalt and platinum, the presence of cerium was unable to be detected by XRD and TEM analysis. The relative histogram of the particle size versus % distribution of metallic NPs is described in Fig. 4(i) and the inset TEM image showed that the as-synthesized metallic NPs have an extremely small size of 2-3 nm. The high-angle annular dark-eld scanning transmission electron microscopic (HADDF-STEM) and the elemental mapping images for the Co 0.97 Pt 0.03 /CeO x /CGO nanohybrid are shown in Fig. 4(j) and (k), respectively. It represented the dispersion of Co, Ce, and Pt elements on the surface of CGO with a higher abundance of Co element. The corresponding energy dispersive X-ray (EDX) spectrum further conrmed the existence of Co, Ce, Pt, C, and O elements in the Co 0.97 Pt 0.03 /CeO x /CGO nanohybrid (Fig. S3 †). The surface functionality and oxidation state of the metallic nanoparticles were investigated by X-ray photoelectron spectroscopy. In Fig. 5(a), the high-resolution C 1s spectrum is deconvoluted into six different components labeled from C-1 to C-6.  57 The XPS investigation of atomic oxygen (O 1s) also conrmed the formation of oxygen functionality on the surface of CGO (Fig. S4 †). The peaks situated at 531.01 eV and 532.40 eV could be assigned to C-O and C]O functional groups, respectively. 57 The summary of functional groups obtained on the surface of CGO is represented in Table S1. † For the Co 0.97 Pt 0.03 /CeO x /CGO nanohybrid, the survey spectrum indicated the unambiguous presence of Co, Ce, and Pt elements (Fig. S5 †). The deconvoluted Co 2p XPS spectra shown in Fig. 5(b) revealed that the elemental cobalt exists in Co(0), Co(II), and  Co(III) valence states with a ratio of 25.5%, 27.1%, and 47.4%, respectively. The peaks with B.E. of 778.08 eV (Co 2p 3/2 ), 780.13 eV (Co 2p 3/2 ), and 795.2 eV (Co 2p 1/2 ) could be attributed to metallic cobalt (Co 0 ), Co 2 O 3 (Co 3+ ), and CoO (Co 2+ ) phases, respectively. The two satellite peaks at 785.6 eV (Co 2p 3/2 ) and 803.96 eV (Co 2p 1/2 ) further conrmed the formation of cobalt oxides (e.g., Co 2 O 3 , CoO, and/or Co 2 O 3 ). 58,59 However, the binding energies for Co 3+ and Co 2+ were found to be wellmatched with the reported value of Co 2+ and Co 3+ cation in the Co 3 O 4 crystal. 59 Therefore, it can be inferred that cobalt exists in the mixed oxide state (Co 3+ /Co 2+ ), similar to the Co 3 O 4 crystal. The core level XPS spectra of Ce 3d is represented in Fig. 5(c); on deconvolution, nearly eight peaks were observed, which was denoted in multiplets of (u) and (v). The peaks labeled as u (901.39 eV), u 00 (907.09 eV), and u 000 (916.93 eV) were observed due to the ionization of the Ce 4+ (3d 3/2 ) energy level, while the peaks labelled with v (882.84 eV), v 00 (888.11 eV), and v 000 (898.24 eV) represented the Ce 4+ (3d 5/2 ) ionization. 60,61 The peaks at u 0 (903.48 eV) and v 0 (885.26 eV) could be attributed to the Ce 3+ oxidation state with the energy level of 3d 3/2 and 3d 5/2 , respectively. The probable percentage of the Ce 3+ and Ce 4+ oxidation states is calculated by comparing the area under each curve and it was observed that nearly 75-80% of Ce (3d) exists in the Ce 4+ oxidation state and the remaining 25-20% portion occupied by the Ce 3+ state. It was well explained that the presence of Ce 3+ can boost the overall catalytic performance by exchanging the lattice oxygen among vicinal cobalt ions, which can promote cobalt ions to a higher valence state. 62,63 This may enhance the rate of dehydrogenation since Co(III) ions can offer more active sites for the dehydrogenation of SB molecules. Lastly, the valence state of platinum was estimated by the deconvolution of the core level XPS spectra of Pt 4f shown in Fig. 5(d). The pair of doublets at 71.72 eV, 74.97 eV (Pt 4f 7/2 ) and 72.42 eV, 75.89 eV (Pt 4f 5/2 ) could be assigned to the Pt(0) and Pt(II) oxidation state, respectively. 15,64 On comparing the relative peak areas, it was found that Pt(0) has more abundance than the Pt(II) component. The observed positive shi in the BE of Pt(0) may be attributed to the chemical interaction between Pt and CGO, cobalt, or cerium ions. 53,64 Thus, from the above, it can be inferred that platinum majorly exists in the metallic form while cobalt and cerium are available in their mixed oxide state. The deconvolution summary of the Co 0.97 Pt 0.03 /CeO x /CGO nanohybrid is represented in Table S2. †

Catalytic ethanolysis of sodium borohydride
The catalytic potential of the as-synthesized Co 0.97 Pt 0.03 /CeO x / CGO nanohybrid has been evaluated for the ethanolysis of SB under alkaline conditions (12 wt% NaOH) at 300 K. The series of nanocomposites with catalytic support (i.e., Co 0.97 /CGO, Co 0.97 / CeO x /CGO, Co 0.97 Pt 0.03 /CGO, CeO x /Pt 0.03 /CGO, and Co 0.97 Pt 0.03 / CeO x /CGO) and without catalytic support (i.e., Co, Co 0.97 /CeO x , Co 0.97 Pt 0.03 , CeO x /Pt 0.03 , and Co 0.97 Pt 0.03 /CeO x ) have been extensively screened for the ethanolysis of SB to determine the catalytic dehydrogenation potential of each constituent ions. The evaluation prole for each combination is shown in Fig. 6(a). Nevertheless, all the metallic compositions have shown promising dehydrogenation potentials but the maximum hydrogen generation rate (HGR) of 41.53 L (min g M ) À1 was obtained with the Co 0.97 Pt 0.03 /CeO x /CGO nanohybrid (Fig. S6 †). This observed enhancement can be explained by Sabatier's principle, 65  the activity prole is shown in Fig. 6(b). It was observed that 100% dehydrogenation has been obtained in all three cases but the highest HGR of 41.53 L (min g M ) À1 was recorded for the Co 0.97 Pt 0.03 /CeO x /CGO nanohybrid (Fig. S7 †). This enhanced catalytic activity may be attributed to the (i) surface functionality present on the CGO, (ii) the availability of mesopores with $6 nm size in the carbon network and the high surface area of CGO (37.12 m 2 g À1 ) compared to CNP that can facilitate the homogenous dispersion of the metallic nanoparticles, and (iii) the high stability of the CGO structure owing to the intercalated graphene oxide layers, which alleviates its agglomeration during the dehydrogenation reactions. In addition to the catalytic support, the solvotic medium has shown a signicant inuence on the hydrogen production [ Fig. S8 †]. Compared to the hydrolysis [21.39 L (min g M ) À1 ], nearly two times higher hydrogen generation was observed with ethanol as a solvotic medium. This inherent acceleration may be ascribed to the better dispersibility of the Co 0.97 Pt 0.03 /CeO x /CGO nanohybrid in ethanol medium and the formation of a non-sticky byproduct, i.e., NaB(OCH 2 CH 3 ) 4 , which reduces the plugging problem in the reactor.
It was already well investigated that the alkaline pH of the reaction medium restricts the self-hydrolysis of SB. The trend of H 2 generation and the respective HGR from the ethanolysis of SB at different concentrations of NaOH is represented in Fig. S9 and S10, † respectively. It was observed that with the increase in NaOH concentration, the rate of hydrogen production increased linearly. However, at higher concentrations, i.e., 12 wt% and 15 wt%, the increment is nearly same, which may be due to the inhibiting effect of hydroxide ions. 27 By virtue of this, we have carried all the dehydrogenation reactions at an NaOH concentration of 12 wt% and the reaction temperature was maintained at 300 K. Thus, from the above evaluation studies, it can be inferred that Co 0.97 Pt 0.03 /CeO x /CGO is the most active nanohybrid for the ethanolysis of SB under alkaline conditions at 300 K. Further, the catalytic performance of the nanohybrid and the kinetics of ethanolysis have been optimized with respect to the concentration of cobalt, the concentration of NaBH 4 , and the reaction temperatures in similar reaction conditions. From Fig. 7(a), it can be seen that the rate of dehydrogenation is proportionality increased with the increase in the cobalt concentration from 0.29 mM to 0.71 mM. The highest hydrogen generation of 142.76 L (min g M ) À1 was obtained for 0.71 mM of cobalt concentration; the respective trend of HGR with respect to cobalt concentration was depicted in Fig. S11. † The reaction order for the ethanolysis of SB at varying [Co] concentrations was determined by plotting the natural logarithmic plot of Co concentration against hydrogen generation [the inset in Fig. 7(a)]. The obtained well-tted straight line with a slope value of 1.16 indicates that the reaction rate of ethanolysis is rst order with respect to cobalt concentration. Similarly, the effect of NaBH 4 concentration on the ethanolysis of SB was studied by varying the initial concentration from 7.93 mM to 18.50 mM under constant reaction conditions, as shown in Fig. 7(b). A constant linear increment in H 2 evolution was observed and the obtained slope value of 6 Â 10 À2 [the inset in Fig. 7(b)] inferred that the ethanolysis of SB follows zero-order kinetics within the given range of NaBH 4 concentration. 66 Furthermore, the effect of temperature on the ethanolysis of SB was investigated by evaluating the nanohybrid at different temperature ranges between 298 K to 313 K. It is quite obvious that with the increase in reaction temperature, the rate of H 2 generation is increased due to the enhancement in catalytic activity. The highest HGR of 52.81 L (min g M ) À1 was obtained at 313 K. The plot of reaction temperature (K) versus the volume of H 2 (mL) is shown in Fig. 8(a) and the change in the value of HG against temperature (K) is depicted in Fig. S12. † The apparent  where, k ¼ reaction rate constant [L (min g) À1 ], A ¼ preexponential factor, E a ¼ activation energy, and T ¼ reaction temperature (K).
The apparent activation energy was calculated by multiplying the slope value of the Arrhenius plot [i.e., the plot between the inverse of reaction temperature, (1000/T (K À1 )), with the natural logarithm of the temperature-dependent rate constant (ln(k)), as shown in the inset of Fig. 8(a)] and the universal gas constant (R). The apparent activation energy (E a ) for Co 0.97 Pt 0.03 /CeO x /CGO was found to be 21.22 kJ mol À1 , which is comparatively lower than many popular cobalt-based composites ( Table 2).
The reusability of the nanohybrid was determined by consequently injecting 13.21 mmol of alkaline SB solution in the same reaction mixture for up to 09 cycles of ethanolysis. Consistent dehydrogenation performance was observed up to 07 cycles with a slightly decreased HGR. The reusability performance of the nanohybrid is represented in Fig. 8(b) and S13. † However, a drastic decline in the HGR was observed in the 08 th and 09 th cycles. This decline in the catalytic activity can be attributed to the excess accumulation of NaB(OC 2 H 5 ) 4 on the catalytic surface, which may deteriorate the active sites of the nanohybrid while also simultaneously poisoning the metallic platinum. Despite the accumulation of the reaction byproducts in the same reactor vessel, nearly 100% dehydrogenation activity has been obtained from the 1 st to 9 th cycle, which itself represents the potential of the nanohybrid for on-board hydrogen production. Simultaneously, the recyclability and % H 2 productivity of a similar composite has been checked for ve runs of ethanolysis of NaBH 4 at similar experimental conditions [ Fig. 9(a) and (b)]. Aer each run, the same catalyst is recovered, washed, and reused for the next run. The composite has shown complete dehydrogenation activity but the overall HGR is steadily decreased, which may due to the continuous deterioration of active sites.

Mechanistic elucidation for the ethanolysis of sodium borohydride
From the physico-chemical characterization of the nanohybrid and the experimental observations, it can be proposed that the evolved H 2 molecule is formed by the combination of H + ions   Fig. 10; each step involved in the dehydrogenation process is illustrated as follows.
The proposed mechanism for the catalytic ethanolysis of SB is summarized as follows: (i) In the Co 0.97 Pt 0.03 /CeO x /CGO nanohybrid, the present mesoporous channels and surface oxygen functionalities on CGO provide an anchoring site for metal cations and simultaneously facilitate the adsorption of ethanol molecules by intermolecular H-bonding.
(ii) The adsorbed ethanol molecules can strongly interact with the available metal oxides, i.e., CeO x and Co 3 O 4 by dipole-  (iv) The hydride ion (H À ) reacts with the proton obtained in Step-I and leads to the formation of the H 2 molecule. (Step-III).
In the case of 100% dehydrogenation, the SB molecules can produce four moles of H 2 . The overall transformation of H 2 formation on the surface of Co 0.97 Pt 0.03 /CeOx/CGO is presented in Step-IV.
The above proposed dehydrogenation pathway reveals that the synergetic interaction between the catalytic support CGO and ternary Co 0.97 Pt 0.03 /CeO x can determine the rate and extent of ethanolysis. In the long term, the simultaneous generation and accumulation of ethoxy borate may hinder the catalytic activity by blocking the active metallic sites and the catalytic activity can be regenerated by the repeated washing of the nanocomposite.

Conclusion
We have demonstrated the applicability of the Co 0.97 Pt 0.03 / CeO x /CGO nanohybrid for the alkaline ethanolysis of SB, which exhibits 100% dehydrogenation activity at 300 K. The experimental investigations indicate that the catalytic support CGO and synergistic interaction among metallic Pt, Co/Co 3 O 4 , and CeO x counterparts are typically responsible for the improved catalytic performance. In the Co 0.97 Pt 0.03 /CeO x /CGO nanohybrid, the available mesoporous channels on CGO and its inherent oxygen functionality particularly facilitate the distribution of metal nanoparticles. Moreover, the intercalated GO layers promote intermetallic charge transport. The characterization details suggest that the nanohybrid is composed of metal oxides, i.e., Co 3 O 4 , CeO x (Ce 4+ /Ce 3+ ), and metallic Co and Pt NPs, which strongly interact with the vicinal C 2 H 5 OH molecule and BH 4 À ions, respectively. On the basis of physicochemical characterization, we have proposed that hydrogen generation from SB is accompanied by a combination of H À from BH 4 À molecules and H + from the C 2 H 5 OH molecule. The kinetic studies of SB ethanolysis suggested that the rate of hydrogen production is proportional to the cobalt concentration and is independent of the SB concentration. Overall, the Co 0.97 Pt 0.03 /CeO x /CGO catalyst has shown unprecedented hydrogen generation rate [41.53 L (min g M ) À1 ], low activation energy [21.42 kJ mol À1 ], and excellent reusability [9 cycles], which makes it a highly competitive catalyst for the ethanolysis of SB. Therefore, we believe that this low-cost Co 0.97 Pt 0.03 /CeO x / CGO nanohybrid has great potential as a dehydrogenation catalyst and can be effectively used for on-board H 2 production.

Conflicts of interest
There are no conicts to declare.