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• The structure and morphology of FeCoNi-S@NF were tuned by cation etching strategy. • The 3D nanoflower structure of FeCoNi-S@NF enhances the number of active sites. • The FeCoNi-S@NF exhibits high FE FDCA in a wide potential from 1.45 to 1.60 V. • The FeCoNi-S@NF exhibits bifunctionality for highly efficient HMFOR and HER. To achieve clean and sustainable energy development, the thermodynamically favourable electrocatalytic oxidation reaction of biomass derivatives can be combined with electrolysis for hydrogen production. This process simultaneously generates high-value 2,5-furandicarboxylic acid and green energy (i.e., hydrogen). The present thesis focuses on the synthesis of a novel Fe-Co-Ni nanosheet catalyst foam using impregnation methods and one-pot hydrothermal techniques. Subsequently, the 3D nanoflower FeCoNi-S@NF catalysts are subsequently prepared by sulfurizing the FeCoNi-LDH@NF precursors. These catalysts were then employed for electrolytic seawater hydrogen production coupled with the electrocatalytic oxidation of 5-hydroxymethylfurfural (HMFOR). This strategy is expected to address the slow kinetics of the oxygen evolution reaction (OER). The 3D nanoflower structure of the FeCoNi-S@NF catalyst enhances the exposure of catalytically active sites, while sulfur doping further improves the electron transfer ability. At a low reaction potential of 1.45 V vs. RHE, FeCoNi-S@NF exhibited remarkable performance with a 95.68 % conversion rate for 5-hydroxymethylfurfural (HMF), a 94.83 % yield for 2,5-furandicarboxylic acid (FDCA), and a Faraday efficiency of 94.71 %. Furthermore, FeCoNi-S@NF exhibits a remarkable response in terms of hydrogen evolution in seawater. By utilizing HMFOR as the anodic reaction and low-cost seawater as the cathodic electrolyte for the hydrogen evolution reaction (HER), simultaneous biomass upgrading and hydrogen production can be achieved. Incorporating HMFOR into a two-electrode system for the electrolytic seawater hydrogen production process significantly reduces the needed voltage (1.70 V@10 mA cm−2), thereby potentially decreasing the cost of this process. [ABSTRACT FROM AUTHOR]

[Display omitted] • NiFe-LDH were grown vertically on the surface of BTO which provided more active sites. • t-BTO@NiFe-LDH has excellent OER property due to the self-polarized ferroelectric t-BTO. • Interface tension between BTO and NiFe-LDH made BTO easily self-polarize, causing band tilting. • The superior OER activity results from the active sites and the optimized d-band center. • The design of a ferroelectric OER electrocatalyst based on self-polarization is provided. A flower-like core–shell heterostructured oxygen evolution reaction (OER) electrocatalyst based on tetragonal BaTiO 3 nanoparticles (t-BTO NPs) and NiFe-layered double hydroxide (NiFe-LDH) nanoarrays was prepared in this study. The influence from the self-polarization effect of t-BTO on the OER performance of NiFe-LDH is reported. Intriguingly, the OER activity of the t-BTO@NiFe-LDH heterojunctions in an alkaline media (1.0 M KOH) exhibited a low overpotential of 186 mV at 10 mA/cm2 and a low Tafel slope of 38.3 mV dec-1, which were far superior to those of the component materials: NiFe-LDH (267 mV and 94.8 mV dec-1) and t-BTO NPs (517 mV and 132.4 mV dec-1). Density functional theory (DFT) calculations revealed that the effective electronic modulation between t-BTO NPs and NiFe-LDH nanoplatelets narrowed the bandgap, promoted the electric conductivity, moderately raised Ed (i.e., energy level of the d-band center), optimized the adsorption ability of the oxygen-containing intermediates (*O, *OH, and *OOH), and induced an apparent reduction in the free energy barrier for the transformation from O* to OOH* in the t-BTO@NiFe-LDH heterojunctions. The PDOS result confirmed that t-BTO in the heterojunctions was easier to polarize, which can cause the rapid electron transfer in the OER process. In these heterostructures, the interface tension between BTO NPs and NiFe-LDH endowed BTO with easier self-polarization, thus leading to greater band tilting and faster electron transfer. Multiple synergistic effects of the flower-like core–shell t-BTO@NiFe-LDH heterojunctions enabled them with higher electrocatalytic activity. This work provides an in-depth understanding of the rational design of a high-efficiency, noble metal-free ferroelectric OER electrocatalyst based on the self-polarization of t-BTO NPs. [ABSTRACT FROM AUTHOR]