A Highly Efficient Nickel Phosphate Electrocatalyst for the Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

Abstract

The electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF), one of biomass-derived platform compounds, is an attractive route to produce 2,5-furandicarboxylic acid (FDCA), an important monomer of bio-based polyesters. Here, we successfully synthesized a highly efficient and stable nickel phosphate (Ni3 (PO4)2) electrocatalyst by a simple hydrothermal method for the electrocatalytic oxidation of HMF to FDCA, in which the yield of FDCA reached 94.2% and the Faraday efficiency was 93.5% in 0.1 M KOH. Compared with nickel hydroxide (Ni (OH)2), the introduction of phosphorus enhanced the charge transfer ability of Ni-based catalysts by EIS and Tafel slope analysis. At the same time, the Ni2+ species in Ni3(PO4)2 was more likely to be oxidized to active nickel species than that in Ni (OH)2 from XPS and in situ Raman results. Moreover, in situ attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) over Ni3(PO4)2 were carried out to study the changes of nickel phosphate during the electrocatalytic oxidation of HMF. According to ATR-SEIRAS, XPS, and Raman results, it can be concluded that Ni2+ species under applied potential in KOH solution was transformed to the high-valence nickel species/Ni3+ species with P–OH and the ring-shaped P–O group. In addition, the phosphorus group was also involved in the electrocatalytic oxidation of HMF. Based on these evidences, a complete electrocatalytic oxidation process of HMF to FDCA on Ni3(PO4)2 was proposed.

Strengthening the Stability of the Reconstructed NiOOH Phase for 5-Hydroxymethylfurfural Oxidation

“…The characteristic peak at 458 cm –1 corresponds to Ni­(OH) 2 . However, 14%Ce-Ni­(OH) 2 shows two wide and weak peaks in the range of 400–650 cm –1 corresponding to the characteristic peaks of Ni–O (480 cm –1 ) and Ni–O–Ce (604 cm –1 ), and no obvious Ce–O is observed, which further proves that Ce is successfully doped into Ni­(OH) 2 (Figure a). , After the sample was activated, the peak position moves to the low-frequency region (471 and 557 cm –1 ), and the peak intensity is obviously enhanced, which is related to the formation of NiOOH . FT-IR spectra of Ni­(OH) 2 , 14%Ce-Ni­(OH) 2 , and activated 14%Ce-Ni­(OH) 2 are shown in Figure S3b.…”

“…In the second LSV curve, only a small peak is observed because part of the Ni­(OH) 2 has been converted into NiOOH, which is consistent with the CV curve. However, after adding 10 mM HMF, the LSV curve shows a higher and wider oxidation peak (0.35–0.65 V vs Ag/AgCl), which is the contribution of HMF oxidation . However, the oxidation peak of Ni­(OH) 2 /NiOOH is covered by the HMF oxidation peak but does not disappear .…”

“…However, after adding 10 mM HMF, the LSV curve shows a higher and wider oxidation peak (0.35−0.65 V vs Ag/AgCl), which is the contribution of HMF oxidation. 31 However, the oxidation peak of Ni(OH) 2 /NiOOH is covered by the HMF oxidation peak but does not disappear. 49 When the potential exceeds 0.6 V vs Ag/AgCl, the linearly increased current is attributed to the superposition of HMF oxidation and OER rather than the separate OER.…”

“…29,30 After the sample was activated, the peak position moves to the low-frequency region (471 and 557 cm −1 ), and the peak intensity is obviously enhanced, which is related to the formation of NiOOH. 31 FT-IR spectra of Ni(OH) 2 , 14%Ce-Ni(OH) 2 , and activated 14%Ce-Ni(OH) 2 are shown in Figure S3b. A broad absorption peak in the range of 3342 cm −1 could be attributed to the O−H stretching vibration of water molecules, and the absorption peak at 1650 cm −1 is due to the angular deformation of water (δ (H−OH) ).…”

Bimetallic nickel/manganese phosphate–carbon nanofiber electrocatalyst for the oxidation of formaldehyde in alkaline medium

“…The presence of Ni 2p3/2 peak at higher binding energy compared to Ni(HO) 2 spectra, 855.7 eV, indicates an increase in the valence state of Ni at the surface. 65 In contrast, determining the Mn oxidation state via Mn 3s is challenging due to the low presence of Mn on the surface. 66 In Fig.…”