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. 2024 Apr 23;15(21):8145-8155.
doi: 10.1039/d4sc01221f. eCollection 2024 May 29.

Redox regulation of Ni hydroxides with controllable phase composition towards biomass-derived polyol electro-refinery

Zhuxin Gui  1 , Yingshuai Jia  1 , Xianping Liao  2 , Tianlan Yan  1 , Boxu Gao  1 , Wenbiao Zhang  1   2 , Li Chen  3 , Qingsheng Gao  2 , Yahong Zhang  1 , Yi Tang  1
Affiliations

Redox regulation of Ni hydroxides with controllable phase composition towards biomass-derived polyol electro-refinery

Zhuxin Gui et al. Chem Sci. .

Abstract

Electrocatalytic refinery from biomass-derived glycerol (GLY) to formic acid (FA), one of the most promising candidates for green H2 carriers, has driven widespread attention for its sustainability. Herein, we fabricated a series of monolithic Ni hydroxide-based electrocatalysts by a facile and in situ electrochemical method through the manipulation of local pH near the electrode. The as-synthesized Ni(OH)2@NF-1.0 affords a low working potential of 1.36 VRHE to achieve 100% GLY conversion, 98.5% FA yield, 96.1% faradaic efficiency and ∼0.13 A cm-2 of current density. Its high efficiency on a wide range of polyol substrates further underscores the promise of sustainable electro-refinery. Through a combinatory analysis via H2 temperature-programmed reduction, cyclic voltammetry and in situ Raman spectroscopy, the precise regulation of synthetic potential was discovered to be highly essential to controlling the content, phase composition and redox properties of Ni hydroxides, which significantly determine the catalytic performance. Additionally, the 'adsorption-activation' mode of ortho-di-hydroxyl groups during the C-C bond cleavage of polyols was proposed based on a series of probe reactions. This work illuminates an advanced path for designing non-noble-metal-based catalysts to facilitate electrochemical biomass valorization.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. (a) Schematic illustration of the catalyst synthesis. SEM images of (b) Bare NF and (c and d) Ni(OH)2@NF-1.0. (e and f) TEM images of Ni(OH)2@NF-1.0 (inset: reduced FFT images of HR-TEM). (g) Line scan measurements of HR-TEM images. (h) In situ Raman spectra of Ni(OH)2@NFs-E at various potentials in 1 M KOH. (i) Intensity ratio of two NiIII–O peaks (I481/I563) calculated from in situ Raman characterization.
Fig. 2
Fig. 2. (a) Conversion of GLY, yield, FE and selectivity of FA for Ni(OH)2@NFs-E at 1.36 VRHE in 10 h. (b) GOR performance of Ni(OH)2@NF-1.0 at various potentials. (c) Five consecutive batch electrolysis (10 h in total) over Ni(OH)2@NF-1.0. (d) LSV curves of Ni(OH)2@NF-1.0 in 1 M KOH with or without 100 mM GLY at the scan rate of 5 mV s−1. (e) LSV curves of Ni(OH)2@NFs-E in 1 M KOH with 100 mM GLY at the scan rate of 5 mV s−1. (f) Comparison of GOR performance with state-of-the-art catalysts.
Fig. 3
Fig. 3. (a) CV curves of Ni(OH)2@NF-1.0 and Ni(OH)2@NF-1.2 in 1 M KOH at the scan rate of 2 mV s−1. (b) In situ Raman spectroscopy of Ni(OH)2@NF-1.0 and Ni(OH)2@NF-1.2 in 1 M KOH at 1.36 VRHE with the injection of 100 mM GLY. (c and d) Multi-potential step curves of Ni(OH)2@NF-1.0 and Ni(OH)2@NF-1.2. (e) Schematic illustration of the catalytic cycle for GOR over NiOOH/Ni(OH)2. (f) The variation of OCP as a function of time with the injection of 100 mM FA for Ni(OH)2@NF-1.0 and Ni(OH)2@NF-1.2. (g) I–t curves of FAOR conducted at 1.36 VRHE in 1 M KOH. (h) Conversion of FA after 10 h FAOR.
Fig. 4
Fig. 4. (a) HPLC elution curves of electrolyte at different times of GOR over Ni(OH)2@NF-1.0. (b) Enlarged HPLC elution curve of electrolyte at 6 h of GOR. (c) Summarized GOR pathway.
Fig. 5
Fig. 5. (a) The variation of OCP as a function of time with the injection of 100 mM 1,2-PG or 1,3-PG over Ni(OH)2@NF-1.0. (b) Probe reactions of 1,2-PG or 1,3-PG over Ni(OH)2@NF-1.0. (c) Reaction process of non-ortho-OH polyol and ortho-OH polyol in electrooxidation. (d) Proposed mechanism of C–C bond cleavage in GOR towards FA over NiOOH/Ni(OH)2.
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