Co Based Transition Metal Oxide Catalysts for

Accepted Article Title: Hierarchical Ni-Co Based Transition Metal Oxide Catalysts for Electrochemical Conversion of Biomass into Valuable Chemicals Authors: Lifang Gao, Yu Bao, Shiyu gan, Zhonghui Sun, Zhongqian Song, Dongxue Han, Fenghua Li, and Li Niu This manuscript has been accepted after peer review and appears as an Accepted Article online prior to editing, proofing, and formal publication of the final Version of Record (VoR). This work is currently citable by using the Digital Object Identifier (DOI) given below. The VoR will be published online in Early View as soon as possible and may be different to this Accepted Article as a result of editing. Readers should obtain the VoR from the journal website shown below when it is published to ensure accuracy of information. The authors are responsible for the content of this Accepted Article. To be cited as: ChemSusChem 10.1002/cssc.201800695 Link to VoR: http://dx.doi.org/10.1002/cssc.201800695

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FULL PAPER Hierarchical Ni-Co Based Transition Metal Oxide Catalysts for Electrochemical Conversion of Biomass into Valuable Chemicals

Abstract: Biomass upgrading into sustainable and valuable fine chemicals is alternative to the state-of-the-art petrochemicals. Typically, conversion of 5-hydroxymethylfurfural (HMF) biomass derivative into 2,5-furandicarboxylic acid (FDCA) has been recognized as an economic and green approach to replace current polyethylene terephthalate-based plastic industry. However, this reaction mostly relies on noble-based catalysts for sluggish aerobic oxidation of alcohol groups. In this work, we report a series of hierarchical Ni-Co based transition metal oxide catalysts for HMF oxidation by electrocatalysis. Comprehensive material characterizations and electrochemical evaluations have been performed. 90% FDCA yield, nearly 100% Faradaic efficiency and robust stability were achieved for NiCo2O4 nanowires. As nonprecious catalysts, Ni-Co based transition metal oxide may open up a type of potential materials for highly efficient electrochemical biomass upgrading.

Introduction Fossil fuel-based fine chemicals are associated with the modern society. For instance, one of the bulk petrochemicals, polyethylene terephthalate (PET) represents state-of-the-art solid basis of plastic industry (~56 million tons/year).[1] However, the key monomer of terephthalic acid is upgraded from fossil fuels so that the frequently discussed issues are the unsustainability and environmental impacts.[2] Biomass is a renewable and abundant carbon resource that has been recognized a promising feedstock to replace traditional fossil fuel for sustainable energy and chemicals.[3] The biomass hydrolysis derivatives, 5hydroxymethylfurfural (HMF) is considered as one of the most attractive platform molecule that can be further transformed into high-value added versatile chemicals.[4] Typically, 2,5furandicarboxylic acid (FDCA) by selective oxidation of HMF, has

[a]

[b]

[c]

L. Gao, Dr. Y. Bao, Dr. S. Gan, Dr. Z. Sun, Z. Song, Prof. D. Han, Dr. F. Li, Prof. L. Niu State Key Laboratory of Electroanalytical Chemistry, c/o Engineering Laboratory for Modern Analytical Techniques, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, Jilin，China. Tel: +86 43185262425 Fax:+86 43185262800 E-mail: [email protected]; [email protected] Y. Bao, S. Gan, Z. Sun, D. Han, L Niu Center for Advanced Analytical Science, c/o School of Chemistry and Chemical Engineering, Guangzhou University, Guangzhou 510006, P.R. China L. Gao, Z. Song University of Chinese Academy of Sciences, Beijing, 100039, China Supporting information for this article is given via a link at the end of the document.

been identified as potential substitute for terephthalic acid to produce bio-based plastics instead of PET.[5] The crucial challenge is the sluggish kinetics for selective oxidation of alcohol groups to carboxylic acid [6]. Electrocatalysis through directly controlling the electron transfer by the applied potential is an effective approach for HMF upgrading at ambient temperature and atmospheric pressure [7]. For example, the Pt/C electrocatalyst was used to oxidize HMF to FDCA where a high selectivity was resulted compared to the heterogeneous catalysis. [2a] The recent progress was achieved by the developed Au/C, Pd/C and bimetallic PdxAuy/C for electrocatalytic oxidation of HMF. [8] The results revealed that Au and Pd played different roles in oxidation of alcohol and aldehyde groups of HMF. The optimized bimetallic catalyst Pd1Au2/C achieved 83% FDCA yield, which is higher than that of individual monometallic catalysts. The significance of this work demonstrated high selectivity originated from AuPd alloys with preferable synergetic effect. The development of non-precious catalysts deserves priority for many electrocatalysis fields and also the scale-up production of FDCA by the well-established electrolysis technology. The earlyproposed NiOOH in fact exhibited the potential for Ni-based catalysts. [9] Recently discovered Ni- and Co-based sulfides and phosphides (e.g. Ni3S2, Ni2P and CoP) have been employed for HMF electrocatalysis oxidation, [10] which were previously mostly explored for water splitting including hydrogen evolution (HER) and oxygen evolution reactions (OER). These catalysts showed both high FDCA yield and Faradaic efficiency (FE). However, a debate similar to OER lies in how is the stability of these catalysts under oxidation condition. [11] These catalysts were possibly converted to their oxides/hydroxide counterpart during the reaction. The progress in development of transition metal-based compounds opened up the promising prospective towards highly efficient noble-metal substituted electrocatalysts for HMF oxidation. In this work, we report hierarchical NixCo3-xO4 catalysts grown vertically on 3D Ni foam (NF), which were fabricated through a low temperature hydrothermal method for electrocatalytic biomass upgrading. Their structures can be controlled from nanosheets to nanowires by tuning the ratio of Ni/Co. All the NixCo3-xO4 samples exhibit activities toward HMF oxidation, where introduction of Co significantly enhances the activity. Among NixCo3-xO4 nanostructures, the NiCo2O4 nanowires is found showing the best performances including both onset potential and current density. Product analysis demonstrates 90% FDCA yield and nearly 100% FE.

Results and Discussion Synthesis and characterization of NixCo3-xO4 electrocatalysts

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Accepted Manuscript

Lifang Gao[a,c], Yu bao[b], Shiyu Gan*[b], Zhonghui Sun[b], Zhongqian Song[a,c], Dongxue Han* [a,b], Fenghua Li[a] and Li Niu[a,b]

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Figure 1. The morphologies of nanostructured Ni xCo3-xO4 catalysts on 3D nickel foam by SEM, (a) NiO, (b) Ni 2 CoO4 , (c) Ni1.5 Co1.5 O4 , (d) NiCo2 O4 and (e) Co3 O4 .

Nanostructured NixCo3-xO4 were prepared on the nickel foam support via a hydrothermal strategy followed by an annealing treatment (see experimental section for details). Their morphologies were examined by the scanning electron microscopy (SEM). As illustrated in Figure 1, distinguished nanostructures for NixCo3-xO4 were observed, depending on the Ni/Co atomic ratio, which were also found varied in their color (Figure S1). Figure 1a presents a nanosheet structure of NiO,

a

b

NiO

(111) (111)

20

NiO(111)

(220) (311) (222) (220) (311)

30

(400)

NiO(220)

*Ni(220)

Ni2CoO4

*Ni(200)

Ni1.5Co1.5O4

*Ni(012)

Intensity (a.u.)

NiCo2O4

*Ni(111)

Co3O4

(511) (440)

(511) (440) (400) (422)

40

NiCo2O4 JCPDS: 20-0781

50

60

70

80

2  (degree) Figure 2. (a) SEM images of representative NiCo2O4 nanowires and element mapping testing. Element mappings for other Ni xCo3-xO4 catalysts are shown in Figure S3. (b) XRD patterns of NixCo3-xO4 catalysts. (Co3O4: JCPDS card No. 42-1467; NiO: JCPDS card No. 47-1039)

which vertically grown on the nickel foam (see Figure S2, the controlled experiment revealed a relatively smooth surface for the bare Ni foam substrate). Upon increasing the Co content (Co: Ni =1:2), the edge of nanosheets tend to convert into nanowires (Figure 1b, Ni2CoO4). While further increasing Co to Co: Ni =1:1, the nanowires become much more apparent at the edge (Figure 1c, Ni1.5Co1.5O4). Fully converted nanowires structure was obtained when the molar content of Co reached 2/3 (Co: Ni =2:1, Figure 1d, NiCo2O4). And the Co3O4 without Ni component shows an assembled nanowire structure (Figure 1e). From the above results, it is speculated that introducing of Co atoms will significantly affect the morphologies of NixCo3-xO4 nanostructure. To further examine the compositions and crystal structures of NixCo3-xO4, EDS mapping and XRD were applied for material characterizations. Figure 2a discloses the EDS mapping of the representative NiCo2O4, which reveals that all the Ni, Co and O elements are uniformly dispersed in the nanowires. The atomic percentages are 14.6% Ni, 23.8% Co and 61.6% O with an atomic ratio close to 1: 2: 4. Similar results are also observed for the other four NixCo3-xO4 oxides with stoichiometry of element distribution (Figure S3). Figure 2b depicts the XRD patterns of NixCo3-xO4 catalysts, where four main diffraction peaks represent to the Ni foam substrate, i.e., Ni (111), Ni (200), Ni (012) and Ni (220). Upon introducing of Co, the intensity of NiO (111) and NiO (220) featured peaks were found gradually weakened till entirely disappeared when “x=0” in NixCo3-xO4. The Ni2CoO4 with relatively low Co content exhibits a cubic NiO dominated crystal structure. With the increase of Co content (Ni1.5Co1.5O4 and NiCo2O4), the characteristic XRD patterns of spinel structure appear gradually. Typically, the NiCo2O4 shows patterns at 19.23˚, 30.65 ˚, 36.2˚, 44.66˚ and 64.41˚corresponding to spinel-type (111), (220), (311), (400), (511) and (440) planes. [12] Meanwhile, the signals of cubic NiO (111) and (220) disappear apparently, suggesting a conversion of cubic to spinel crystallinity. However, Co3O4 nanowires (Ni was completely replaced by Co) shows welldefined diffraction patterns indexed to (111), (220), (311), (222), (400), (422), (511), and (440) planes, referring to a cubic crystallite.[13] Overall, the above results confirmed the synthesis of the hierarchical NixCo3-xO4 catalysts series and the ratio of Co/Ni has a significant effect on the crystal structure of the samples.


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Electrochemical activity of NiXCo3-XO4 for HMF oxidation The electrocatalytic activities of NiXCo3-XO4 for HMF oxidation were firstly explored by a three-electrode system (Figure 3a). The HMF oxidation occurs at the anode (catalyst working electrode) while the HER occurs at the cathode (carbon rod, counter electrode). A porous ceramic was used for separating the two compartments. Figure 3b shows linear sweep voltammogram a

b

25

-2

J (mA cm )

20

0.1 M KOH 0.1 M KOH+10 mM HMF HMF Oxidation

15 10 5

Ni

0 1.1

1.2

1.3

2+/3+

1.4

1.5

1.6

E (vs RHE) 25

2

J (mA/cm )

20

d

NiO Ni2CoO4

NiO Ni2CoO4 Ni1.5Co1.5O4

NiCo2O4

15

15

Ni1.5Co1.5O4

J (mA/cm2)

c

Co3O4

10

10

NiCo2O4 Co3O4

5

HMF oxidation products analysis and catalytic routes

5 0 1.1

1.2

1.3

1.4

E (vs RHE)

1.5

1.6

0

species can improve the kinetics (or electron transfer coefficient) for HMF oxidation. This is consistent with the observation of an increase of catalytic current for Ni2+/3+ redox peak after introduction of HMF (Figure 3b). On the other hand, the onset potential becomes lower with increase of the Co content (Figure 3c), suggesting that the Co is also a key element. The Tafel slope and onset potential indicate that both Ni and Co elements are essential ingredients, which play a significant role to achieve the synergistic catalytic effect. We further used cyclic voltammetry measurements by extracting electric double layer capacitance to estimate the electrochemically active surface areas (ECSA). As shown in Figure S6, the capacitances of NiO, Ni2CoO4, Ni1.5Co1.5O4, NiCo2O4 and Co3O4 are 1.1 mF cm−2, 1.2 mF cm−2, 3.6 mF cm−2, 16.8 mF cm−2 and 12.3 mF cm−2, respectively. NiCo2O4 exhibits the highest ECSA and thus exposes more active sites for HMF oxidation. We will further demonstrates the NiCo2O4 shows the lowest charge transfer resistance by impedance in the kinetic analysis section. In Figure 3d, the catalytic current density from 1.30 V to 1.45 V of each NiXCo3-XO4 catalyst was compared, in which NiCo2O4 shows the optimal electrochemical performance.

1.30

1.35

1.40

1.45

E (vs RHE)

Figure 3. (a) A schematic illustration of HMF electrocatalysis by NixCo3-xO4 catalysts. (b) The LSV for the NiCo2O4 catalysts at a scan rate of 2 mV s -1 in 0.1 M KOH without and with 10 mM HMF. (c) A comparison of HMF oxidation LSVs at five NixCo3-xO4 catalysts. (d) A comparison of HMF oxidation current density at the potential between 1.35 and 1.45 V.

(LSV) curves of a representative NiCo2O4 catalyst electrode in 0.1 M KOH with and without HMF. It can be seen that the catalyst itself shows a typical redox peak of Ni2+/3+ at 1.38 V (vs RHE, black curve) [14] and the water oxidation starts after 1.55 V. As shown in Figure S4, the other NiXCo3-XO4 catalysts reveal similar electrochemical behavior except Co3O4, whose redox peak can hardly be observed. Upon adding 10 mM HMF, the current increases remarkably at 1.35 V (red curve, Figure 3b) indicating HMF oxidation by the electro-generated Ni3+. The oxidation of water is either suppressed. Subsequently, the catalytic activities for the five NiXCo3-XO4 catalysts were further compared (Figure 3c). It is performed that NiO shows a weak catalytic ability with high onset potential (> 1.45 V) and low catalytic current density (< 5 mA cm-2). After introducing of Co, varying degrees of onset potential and oxidation current density increasing occurred, for example Ni2CoO4 exhibits 150 mV improved onset potential and much higher current density (yellow curve). The activity further increases with the increasing of Co content in Ni XCo3-XO4, while decreases dramatically for Co3O4. The Tafel slope for HMF oxidation was further examined as shown in Figure S5. The Tafel slopes were determined for NiO (47 mV dec-1), Ni2CoO4 (113 mV dec-1), Ni1.5Co1.5O4 (261 mV dec1 ), NiCo2O4 (238 mV dec-1) and Co3O4 (447 mV dec-1). The NiO shows the lowest slope. With decreasing Ni content, the overall trend for the Tafel slope becomes higher, indicating that Ni

Since NiCo2O4 was found to exhibit preferable activity than the other NixCo3-xO4 family members, thus it is chosen for further oxidation product analysis. According to the fundamental inspection shown in Figure 3b, 1.55 V vs RHE was selected since this potential can maintain the maximum oxidation of HMF and the minimum of water oxidation. Based on the calculations, the stoichiometric amount of charge required to completely convert of the given HMF to FDCA was ~35 C (Figure S7). High performance liquid chromatography (HPLC) was used to detect the oxidation products, through which the intermediates of HMFCA, DFF and FFCA as well as the final product of FDCA were determined during the electrolysis (Figure S8). The conversion/yield

Figure 4 (a) Conversion and yield (%) of HMF oxidation by NiCo2O4 catalyst with passed charges at 1.55 V vs RHE. (b) Faradaic efficiency for five cyclic tests. (c) Two possible pathways for HMF oxidation to FDCA.


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a

8

-Z'' (ohm)

6

-Z'' (ohm)

60

40

NiO

20

0

Kinetic analysis To further investigate the catalytic kinetics regarding to HMF electrochemical oxidation, the electrochemical impedance spectroscopy (EIS) measurements were carried out. Figure 5a displays the Nyquist plots of NixCo3-xO4 catalysts in KOH electrolyte containing HMF at the potential of 1.45 V vs RHE. Typically, each plot shows a semicircle in the high frequency associated with the charge transfer and a linear region in low frequency related to the diffusion behavior. [16] It is observed that NiO only shows a semicircle without diffusion region, which indicates an intrinsic slow kinetic of NiO (inset in Figure 5a). Subsequently, an equivalent circuit was used for fitting the Nyquist plots (Figure 5b), which includes Rs (series resistance), Rct (charge transfer resistance), Qdl (double-layer capacitance) and Zw (Warburg resistance). All the fitted parameters are shown in Figure 5c. It is found that the crucial Rct follows the order: NiCo2O4 < Ni1.5Co1.5O4 < Ni2CoO4 < Co3O4 < NiO. This trend is quite consistent with that of HMF oxidation current density (Figure 3d), which demonstrates the fast ET contributed by NiCo2O4. Although a high Rct is observed for pure NiO, it decreases remarkably upon the introduction of Co. The results indicate that Co immigrant can greatly improve the charge transfer kinetic of NixCo3-xO4 catalysts and facilitate the mass transfer. [17] However, the Rct increased without Ni (see Co3O4) which further indicates the synergic functions of Ni and Co species. Stability examination

50

100

150

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250

Z' (ohm)

4 Ni2CoO4

2

Ni1.5Co1.5O4 NiCo2O4 Co3O4

0 30

35

40

45

50

Z' (ohm) b

Generally, upon the evaluation of catalytic activity, cycling durability should be regarded as another significant principle assessing the electrochemical performance. Figure 4b exhibits an advisable FE (92-99%) for five successive cyclic electrolysis, which suggested a fair cycling stability for NiCo2O4. To gain more insights of the catalyst nature, variation of compositions and structure of the NiCo2O4 catalyst were further examined after five cycle electrolysis tests. SEM images depicted in Figure 6 revealed a preserved nanowire array structure. The elemental mapping further indicated a uniformly distribute of Ni, Co and O elements.

c

Figure 6. SEM images of NiCo2O4 and element mapping images after five cycle tests. Figure 5. (a) Nyquist plots for NixCo3-xO4 catalysts in 0.1 M KOH and 10 mM HMF under potential 1.45 V vs RHE. Amplitude: 10 mV. Frequency: 0.01105 Hz. Inset show the Nyquist plot of NiO. (b) The proposed equivalent circuit. (c) Corresponding fitted parameters. Rs and Rct: ohm. Q dl: Ω-1·Sn. Zw: Ω -1·S1/2.


Accepted Manuscript

according to different charges are shown in Figure 4a. the yield for the final product FDCA is measured up to 90%, and the FE is between 92% and 99% during five continual measurements (Figure 4b). Based on the calibration curves for the stardand products (Figure S9a-e), the actual values of the products were shown in Figure S9f. The optical images in Figure S7 and Figure S10 show the electrochemical system after electrolysis where the yellowed HMF solution disappeared in the working electrode chamber and bubbles can be observed from the counter electrode (H2 production). Additionally, the carbon balance of HMF during the charge passed presented in Figure S11 further proved the high FE of FDCA. Here two possible well-identified pathways for conversion of HMF to FDCA has been proposed and shown in Figure 4c. One is oxidation of aldehyde group in priority to form HMFCA intermediate, while the other is oxidation of alcohol group to produce DFF intermediate instead. [15] [8] According to the results of HPLC shown in Figure 4a, during the electrolysis only trace DFF was detected while HMFCA showed a much higher concentration. It is identified that the HMFCA intermediate pathway should be considered as the priority mechanism for electrochemical oxidation of HMF.

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780

890

880

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860

O3

fresh

post

850

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534

Binding Energy (eV)

531 eV

532

529 eV

2+

post

780 eV

786 eV

790

782 eV

798 eV

800

Binding Energy (eV)

2+

530

528

Binding Energy (eV)

Figure 7. (a-c) XPS spectrum of the Co2p (a, b), Ni 2p (c, d) and O1s (e, f) of NiCo2 O4 before and after cyclic electrolysis

The XPS spectroscopy was used to further explore the valence state variation of the NiCo2O4 before and after cyclic electrolysis, where high-resolution Co2p, Ni2p and O1s spectrum are mainly examined (Figure 7). The Co2p spectra can be fitted into two types, Co2p3/2 and Co2p1/2 both including Co2+ and Co3+ species (Figure 7a). There are no apparent differences observed before and after reaction, which suggests the invariability for the Co valence state. Similar to Co2p, the Ni2p spectra can also be fitted mainly into Ni2p3/2 and Ni2p1/2 where both Ni2+ and Ni3+ are found only exist in the fresh NiCo2O4 (Figure 7b). However, the Ni2+ components were not detected after electrolysis, which indicates that all of Ni2+ were converted into Ni3+ after electrolysis. This valence state change further suggests that the Ni3+ or even higher valence state Ni content might serve as the real HMF catalytic site, which has been reported in previous Ni-based electrocatalyst for water oxidation. [10c, 18] For the O1s spectra, three main components were fitted including O1 band at 529.3 eV, O2 band at 531.1 eV and O3 band at 532.5 eV (Figure 7c). The O1 band is ascribed to metal-oxygen bond and the O2 band represents the oxygen in OH- groups. [19] The O3 band is due to some oxygen ions in low coordination or physi- and chemisorbed water at the surface. [19] It is found that the O1 band decreases significantly while O2 band increases after electrolysis. This result demonstrates that the metal-oxygen bond was converted into metal oxyhydroxide. In combination with the Ni2p spectra, it can be speculated that the Ni-O bond was transformed into Ni-OOH bond, which further supports the active site of Ni3+ or higher Ni species for oxidation HMF into FDCA. [20] It should be noted that Co should play a synergic role associated with Ni toward HMF oxidation although no apparent changes were observed. The introduction of Co might change the electronic structure of Ni, which is similar to the Fe to improve the water oxidation sufficiently for Ni based oxyhydroxides. [21] Overall, these investigations confirmed the favorable stability property of NiCo2O4 catalyst. Ni species should act as the active sites while Co plays a synergic function.

Conclusions In summary, a series of hierarchical NixCo3-xO4 nanostructures have been synthesized and applied as electrocatalysts for HMF oxidation. All the catalysts exhibit considerable activities and the introduction of Co initiated significant improvement in the catalytic kinetics. At the appropriate doping level, NiCo2O4 nanowires exhibited the best performances of nearly 90% FDCA yield, 100% FE and satisfactory stability. Such Ni-Co based electrocatalysts open a promising prospective for biomass and chemical energy conversion in an economic and green approach.

Experimental Section Materials and chemicals 5-Hydroxymethyl-2-furaldehyde

(99%),

5-hydroxymethyl-2-

furancarboxylic acid (98%) were purchased from Shanghai Shuya Corp. 2,5-Difoemyfuran (98%), 2,5-Furandicarboxylic acid (98%), Ni(NO3)2· 6 H2O (98%) and Co(NO3)2· 6 H2O (98%) were obtained from Aladdin. CO(NH2)2 was bought from Alfa, and NH4F was got from Beijing Chemical Reagent Corp. Nickel foam was purchased from Shenzhen Green and Creative Environmental Science and Technology Co., Ltd. Deionized water (DI water, 18 MΩ cm -1) was purified through a Millipore system. All the chemicals used in the experiments were at least of analytical grade and were used without further purification.

Physical characterizations X-ray diﬀraction (XRD) analysis was performed on a at D8 Advance (Bruker) system using Cu Kα radiation resource (λ=1.54 angstrom). The chemical states were investigated by the ESCALAB MKII X-ray photoelectron spectrometer using monochromated Al Kα X-ray. The morphology was acquired by using an XL 30 ESEM FEG field emission system operating at 10 KV, and an energy-dispersive X-ray spectroscopy (EDS) attachment was used to obtain the surface element composition of synthesized samples. Synthesis of NixCo3-xO4 catalysts


Accepted Manuscript

810

795 eV

post

fresh

O2

532 eV

3+

2+

O1

O 1s

3+

Intensity (a.u.)

Sat.

Sat.

3+

855 eV 854 eV

3+

2+

Sat.

c

Ni 2p 3/2

Ni 2p 1/2

861 eV

Sat.

Intensity (a.u.)

fresh

803 eV

Intensity (a.u.)

Co 2p 3/2

Ni 2p

874 eV

b

872 eV

Co 2p 1/2

Co 2p

880 eV

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FULL PAPER A facile hydrothermal process was employed for synthesis of Ni xCo3-

calibration curve method, those standards were pure component with

xO 4

a known concentration. The conversion of HMF (%) and yield (%) of

nanostructures with different morphologies on the nickel foam

substrate. Typically, Ni foam (1 cm × 3cm) was cleaned by sonication

the oxidation products were calculated as following:

sequentially in acetone, 3 M HCl, DI water, and ethanol for 15 min HMF consumed (%) =

each before use. Taking NiCo 2O4 nanowires as example, 1mmol of Ni(NO3)2·6 H2O, 2mmol of Co(NO 3)2·6 H 2O, 6 mmol of NH 4F and

yield of product (%) =

15 mmol of urea were dissolved into 36 mL of ultra-pure water, followed by vigorous stirring at room temperature for hours until a

𝑚𝑜𝑙 𝑜𝑓 𝐻𝑀𝐹 𝑐𝑜𝑛𝑠𝑢𝑚𝑒𝑑 𝑚𝑜𝑙 𝑜𝑓 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝐻𝑀𝐹 mol of product formed mol of initial HMF

× 100 × 100

The Faradaic efficiency of FDCA was calculated using the equation:

uniform solution was obtained. Subsequently, the solution and preFE (%) =

processed Ni foam were transferred into a Teflon-lined stainlessroom temperature, the Ni foam was taken out and rinsed thoroughly

× 100

-1

where F is the Faraday constant (96,485 C mol ).

with DI water and ethanol successively several times under the assisted of ultrasound. The self-supported NF/NiCo-precursor was then dried in a vacuum oven at 60 oC for 8 h, and subsequently annealed at 350 oC in Ar atmosphere for 2 h to achieve the final nanostructure. For comparison, a series of Ni xCo 3-xO 4 candidates were synthesized by tuning the feeding molar ration of Ni(NO 3)2·6 H2O and Co(NO3)2· 6 H2O to 1:0, 2:1, 1:1, 1:2 and 0:1, with the corresponding products marked as NiO, Ni2CoO4, Ni1.5Co 1.5O 4, NiCo2O 4 and Co3O4, respectively. Electrochemical experimental Electrochemical measurements were all performed with a CHI 920e

Acknowledgements This work was supported by NSFC, China (21622509, 21475122, 21505127, 21527806, 21627809, 21405147 and 21727815), Department of Science and Techniques of Jilin Province (20160201008GX), Jilin Province Development and Reform Commission (2016C014, 2017C053-1), Science and Technology Bureau of Changchun (15SS05). Keywords: Ni-Co metal oxides • electrocatalysis • Biomass upgrading

electrochemical analyzer (CH Instruments, Inc, Shanghai). All the tests in the three-electrode cell were carried out in a divided cell with NF/Ni xCo3xO4

as working electrode, saturated calomel electrode (SCE) as reference

[1] [2]

electrode and a carbon rod as the counter electrode, respectively. LSV was measured with the scan rate of 2 mV/s in the electrolyte of 0.1 M KOH

[3]

with and without 10 mM organic substrate. iR compensation was used to corrected the LSV data, which determined by a CHI 920e via the resistance test. All the data were presented relative to a reversible hydrogen electrode (RHE). The conversion between potential versus SCE and RHE should refer to the followed equation:

[4]

E (vs RHE) = E (vs SCE) + 0.059 × pH Electrochemical impedance spectroscopy (EIS) measurements were

[5]

performed using a Solartron 1255B Frequency Response Analyzer (Solartron Inc., UK) at a bias potential of 1.45V vs RHE with AC amplitude of 10 mV. The impedance spectra were recorded in a range of frequency from 100 kHz to 0.01 Hz.

[6]

HPLC analysis of the oxidation products The electrocatalytic oxidation of HMF based on the three-electrode reaction was performed in a divided-cell with a gentle stir under potential of 1.55 V vs RHE. 10 µL of the electrolyte was extracted and diluted to 500 µL with DI water. The sample solution was then

[7]

analyzed by high-performance liquid chromatography (HPLC) (Agilent) using a UV detector set at 265 nm and a waters-organic acid column. The analysis was obtained under the following condition:

[8]

mobile phase 5 mM H2SO4; flow rate 0.5 mL min -1; column temperature 333 K. The identification and quantification of the oxidation products were calculated by the external standard

[9]

R. A. Sheldon, Green Chem. 2014, 16, 950-963. a) K. R. Vuyyuru, P. Strasser, Catal. Today 2012, 195, 144-154; b) A. Corma, S. Iborra, A. Velty, Chem. Rev. 2007, 107, 2411-2502. a) Y. Román-Leshkov, C. J. Barrett, Z. Y. Liu, J. A. Dumesic, Nature, 2007, 447, 982; b) D. R. Dodds, R. A. Gross, Science 2007, 318, 1250; c) R. S. Wishart, Science, 1978, 199, 614-618; d) A. J. Ragauskas, C. K. Williams, B. H. Davison, G. Britovsek, J. Cairney, C. A. Eckert, W. J. Frederick, J. P. Hallett, D. J. Leak, C. L. Liotta, Science 2006, 311, 484489; e) K. Gupta, R. K. Rai, S. K. Singh, ChemCatChem 2018,10，1-25. a) T. Wang, M. W. Nolte, B. H. Shanks, Green Chem. 2014, 16, 548-572; b) R. J. van Putten, J. C. van der Waal, E. de Jong, C. B. Rasrendra, H. J. Heeres, J. G. de Vries, Chem Rev. 2013, 113, 1499-1597. a) C. Moreau, M. N. Belgacem, A. Gandini, Top. Catal. 2004, 27, 11-30; b) A. Eerhart, A. Faaij, M. K. Patel, Energy Environ. Sci. 2012, 5, 64076422; c) A. Gandini, A. J. D. Silvestre, C. P. Neto, A. F. Sousa, M. Gomes, Journal of Polymer Science Part A: Polym. Chem. 2009, 47, 295-298; d) A. J. J. E. Eerhart, A. P. C. Faaij, M. K. Patel, Energy Environ. Sci. 2012, 5, 6407. a) M. A. Lilga, R. T. Hallen, M. Gray, Top. Catal. 2010, 53, 1264-1269; b) Z. Zhang, K. Deng, ACS Catal. 2015, 5, 6529-6544; c) C. V. Nguyen, Y.-T. Liao, T.-C. Kang, J. E. Chen, T. Yoshikawa, Y. Nakasaka, T. Masuda, K. C. W. Wu, Green Chem. 2016, 18, 5957-5961; d) O. Casanova, S. Iborra, A. Corma, ChemSusChem 2009, 2, 1138-1144; e) A. Villa, M. Schiavoni, S. Campisi, G. M. Veith, L. Prati, ChemSusChem 2013, 6, 609-612. a) Y. Kwon, K. J. P. Schouten, J. C. van der Waal, E. de Jong, M. T. M. Koper, ACS Catal. 2016, 6, 6704-6717; b) T. Cao, M. Wu, V. V. Ordomsky, X. Xin, H. Wang, P. Metivier, M. Pera-Titus, ChemSusChem 2017, 10, 4851-4854. D. J. Chadderdon, L. Xin, J. Qi, Y. Qiu, P. Krishna, K. L. More, W. Li, Green Chem. 2014, 16, 3778-3786. G. Grabowski, J. Lewkowski, R. Skowroński, Electrochim. Acta 1991, 36, 1995.


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steel autoclave and kept at 120 oC for 12h. After naturally cooled to

𝑚𝑜𝑙 𝑜𝑓 𝐹𝐷𝐶𝐴 𝑓𝑜𝑟𝑚𝑒𝑑 𝑡𝑜𝑡𝑎𝑙 𝑐ℎ𝑎𝑟𝑔𝑒 𝑝𝑎𝑠𝑠𝑒𝑑/(𝐹×6)

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[11]

[12] [13] [14]

[15]

a) N. Jiang, B. You, R. Boonstra, I. M. Terrero Rodriguez, Y. Sun, ACS Energy Lett. 2016, 1, 386-390; b) B. You, N. Jiang, X. Liu, Y. Sun, Angew. Chem., Int. Ed. 2016, 55, 9913-9917; c) B. You, X. Liu, X. Liu, Y. Sun, ACS Catal. 2017, 7, 4564-4570; d) B. You, X. Liu, N. Jiang, Y. Sun, J. Am. Chem. Soc. 2016, 138, 13639-13646. a) S. Jin, ACS Energy Lett. 2017, 2, 1937-1938; b) A. Dutta, A. K. Samantara, S. K. Dutta, B. K. Jena, N. Pradhan, ACS Energy Lett. 2016, 1, 169-174; c) L.-A. Stern, L. Feng, F. Song, X. Hu, Energy Environ. Sci. 2015, 8, 2347-2351. L. Qian, L. Gu, L. Yang, H. Yuan, D. Xiao, Nanoscale 2013, 5, 7388-7396. Z. Chang, H. Dou, B. Ding, J. Wang, Y. Wang, X. Hao, D. R. MacFarlane, J. Mater. Chem. A 2017, 5, 250-257. a) X. Lu, C. Zhao, Nat. Commun. 2015, 6, 6616; b) M. Gao, W. Sheng, Z. Zhuang, Q. Fang, S. Gu, J. Jiang, Y. Yan, J. Am. Chem. Soc. 2014, 136, 7077-7084. H. G. Cha, K. S. Choi, Nat. Chem. 2015, 7, 328-333.

[16] [17]

[18] [19] [20] [21]

H. Heli, H. Yadegari, Electrochim. Acta 2010, 55, 2139-2148. Q. X. Xia, K. San Hui, K. N. Hui, S. D. Kim, J. H. Lim, S. Y. Choi, L. J. Zhang, R. S. Mane, J. M. Yun, K. H. Kim, J. Mater. Chem. A 2015, 3, 22102-22117. B. You, N. Jiang, M. Sheng, M. W. Bhushan, Y. Sun, ACS Catal. 2015, 6, 714-721. J. F. Marco, J. R. Gancedo, M. Gracia, J. L. Gautier, E. Ríos, F. J. Berry, J. Solid State Chem. 2000, 153, 74-81. R. D. Smith, C. P. Berlinguette, J. Am. Chem. Soc. 2016, 138, 1561-1567. S. L. Candelaria, N. M. Bedford, T. J. Woehl, N. S. Rentz, A. R. Showalter, S. Pylypenko, B. A. Bunker, S. Lee, B. Reinhart, Y. Ren, S. P. Ertem, E. B. Coughlin, N. A. Sather, J. L. Horan, A. M. Herring, L. F. Greenlee, ACS Catal. 2016, 7, 365-379.


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10.1002/cssc.201800695

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FULL PAPER FULL PAPER Lifang Gao[a,c], Yu bao[b], Shiyu Gan*[b], Zhonghui Sun[b], Zhongqian Song[a,c], Dongxue Han* [a,b], Fenghua Li[a]and Li

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Hierarchical Ni-Co Based Transition Electrochemical conversion of renewable biomass into value added chemicals and clean fuels by Ni-Co based transition metal oxide non-precious catalysts.

Metal Oxide Catalysts for Electrochemical Conversion of Biomass into Valuable Chemicals

[a]

This article is protected by copyright. All rights reserved. [b]

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Niu[a,b]

L. Gao, Dr. Y. Bao, Dr. S. Gan, Dr. Z. Sun, Z. Song, Prof. Dr. F. Li, Prof. L. Niu State Key Laboratory of Electroanalytical Chemistry,c/o E Laboratory for Modern Analytical Techniques, Changchun of Applied Chemistry, Chinese Academy of Sciences, Ch 130022, Jilin， China. Tel: +86 43185262425 Fax:+86 43185262800 E-mail: [email protected], [email protected] Y. Bao, S. Gan, Z. Sun, D. Han, L Niu