Integrating single-cobalt-site and electric field of boron nitride in dechlorination electrocatalysts by bioinspired design

Abstract

The construction of enzyme-inspired artificial catalysts with enzyme-like active sites and microenvironment remains a great challenge. Herein, we report a single-atomic-site Co catalyst supported by carbon doped boron nitride (BCN) with locally polarized B-N bonds (Co SAs/BCN) to simulate the reductive dehalogenases. Density functional theory analysis suggests that the BCN supports, featured with ionic characteristics, provide additional electric field effect compared with graphitic carbon or N-doped carbon (CN), which could facilitate the adsorption of polarized organochlorides. Consistent with the theoretical results, the Co SAs/BCN catalyst delivers a high activity with nearly complete dechlorination (~98%) at a potential of -0.9 V versus Ag/AgCl for chloramphenicol (CAP), showing that the rate constant (k) contributed by unit mass of metal (k/ratio) is 4 and 19 times more active than those of the Co SAs/CN and state-of-the-art Pd/C catalyst, respectively. We show that Co single atoms coupled with BCN host exhibit high stability and selectivity in CAP dechlorination and suppress the competing hydrogen evolution reaction, endowing the Co SAs/BCN as a candidate for sustainable conversion of organic chloride.

Fig. 1. DFT calculations of Co SAs/BCN.

a Electrostatic surface representation of the Rdh; the potential contour was scaled to +5.0 (blue) and −5.0 (red) k_BTe⁻¹ (where k_B is the Boltzmann constant, T is temperature, and e is the charge of an electron). b Electron density plots of BCN with the electric field around B–N bond; the isosurface contours reveal discontinuity in electron density between the N (negative charged) and B (positive charged) atoms. c Orbital density images of C atoms in BCN. d HOMO and e LUMO of isolated Co atom supported on BCN. f PDOS plot of BN-2p and C-2p orbitals. g PDOS plot of Co-3d orbitals; the peaks were imaged in d, e.

Fig. 2. Preparation and characterization of Co SAs/BCN.

a Schematic illustration of the formation of single-atom catalyst with atomically dispersed Co sites and polarized supports. b TEM image of Co SAs/BCN. c, f HAADF-STEM image of Co SAs/BCN (inset: SAED image). d 3D isolines and atom-overlapping Gaussian-function fitting mapping of the square from f and intensity profile along X–Y in f. e EELS element mapping. g Synchrotron X-ray three-dimensional computed tomographic images of Co SAs/BCN.

Fig. 3. Chemical state and coordination information for Co SAs/BCN.

a B K-edge, b N K-edge, and c C K-edge XANES spectra of Co SAs/BCN. d–f High-resolution XPS of N 1s (d), B 1s (e), and Co 2p (f) for Co SAs/BCN sample. g XANES spectra, h Fourier transform (FT) at the Co K-edge of Co SAs/BCN, CoO, and Co foil. i Corresponding EXAFS fitting curves of Co SAs/BCN at R space. The inset of i is the schematic model of Co SAs/BCN, Co (orange), N (blue), B (pink), and C (gray).

Fig. 4. Catalytic mechanism of CAP electrocatalytic dechlorination.

a, b Dechlorination ratio of CAP on various cathode potentials and at different pHs over the Co SAs/BCN, respectively. c Dechlorination ratio of CAP on various catalysts after 3 h electrolysis at −0.9 V. d Plot of the energy difference E_CAP* − E_H* against the E_CAP*; detailed structures are given for BCN-1 and BCN-2 (Supplementary Fig. 22), Co SAs/BCN-1 to −4 (Supplementary Fig. 32), CN-1, CN-2, and Co SAs/CN (Supplementary Fig. 36). e Energy diagrams and intermediate states of CAP dechlorination on the Co SAs/BCN; the optimized structures are detailed in Supplementary Fig. 33. f Faradaic efficiency (FE) of CAP reduction. Left axis denotes the FE of CAP dechlorination (histogram). Right axis denotes the total FE of CAP reduction (dashed line), including the dechlorination reaction and the NO₂ reduction of CAP. g, h Differential pulse voltammetry (DPV) curves of the commercial Pd/C and Co SAs/BCN, respectively, in solutions of 0.5 M H₂SO₄ with dose of CAP and t-BuOH.