Restricting proton transfer via carbon nanohorn-supported monomolecular cobalt phthalocyanine enhances CO2-to-CO electrocatalysis in acidic media

doi:10.1016/S1872-2067(26)65157-1

Abstract

Abstract:

Electrocatalytic reduction of CO₂ to CO in acidic media is a compelling approach toward closing carbon cycle, as it can increase CO₂ utilization while circumvent carbonate precipitation. Nonetheless, a cardinal challenge remains the inherent competition from hydrogen evolution reaction (HER), driven by high proton availability at catalyst surface, which severely suppresses CO₂ reduction selectivity and activity. Herein, we engineer a catalyst comprising monomolecularly dispersed cobalt phthalocyanine on carbon nanohorns (CNHs) with abundant topological defects, which orchestrates efficient CO₂ electroreduction in acidic media via restricting proton transfer. This design constructs an electron-deficient Co center and surrounded with a proton-deficient microenvironment, achieving CO electrogeneration with 95.9% Faradaic efficiency (FE) and 259.1 mA cm^-2 partial current density at pH = 0.5 while maintaining > 85% FE across 38 h durability at pH 1. Mechanistic investigations reveal that the CNHs support simultaneously restricts both key proton-supply pathways: the defect-rich structure suppresses surface hydrogen spillover along the carbon framework, while the dahlia-like architecture of CNHs aggregate hinder axial hydronium diffusion from the bulk electrolyte. The resulting reduction in proton availability around Co centers, combined with limited hydronium access from the bulk, stabilizes crucial *COOH and *CO intermediates and accelerates CO₂ reduction kinetics. By showcasing how carbon-support engineering can modulate proton-transfer pathways, this work offers a viable and generalizable strategy toward high-performance CO₂ electrolysis in strongly acidic media, advancing the design of robust molecular catalysts for practical application.

Key words: Cobalt phthalocyanine, Carbon nanohorns, Acidic CO₂ electrocatalysis, Hydrogen spillover, Restricted proton transfer

Chunchun Wang, Yang Ge, Xindong Song, Yiqi Ding, Zhuo Xing, Ying Yu. Restricting proton transfer via carbon nanohorn-supported monomolecular cobalt phthalocyanine enhances CO₂-to-CO electrocatalysis in acidic media[J]. Chinese Journal of Catalysis, 2026, 89: 390-401.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(26)65157-1

https://www.cjcatal.com/EN/Y2026/V89/I10/390

Figures/Tables 5

Fig. 1. Synthesis and structural characterization of monomolecularly dispersed CoPc on CNHs. (a) Schematic illustration showing CoPc molecules immobilized on CNHs. (b) Raman spectra. (c) TEM image and structure diagram (inset) of CoPc/CNHs-3 catalyst. (d) HRTEM images of CoPc/CNHs-3 catalyst. (e) The AC-TEM image of CNHs fragment. (f) FFT filtered image of the selected area (red box), with pentagonal and hexagonal carbocycles marked in white and red, respectively. (g) HAADF-STEM image from 4D-STEM of CoPc/CNHs-3 catalyst with many single Co atoms (bright dots) distributed. Average Co atomic density is roughly 1.38 ± 1.13?atom nm-2. (h) EDX mapping of CoPc/CNHs-3 catalyst.

Fig. 2. Electronic structure and coordination environment characterization. High-resolution XPS spectra of Co 2p (a), N 1s (b), and C 1s (c) for CoPc/CNHs-3, CoPc, and CNHs catalysts. Co K-edge XANES spectra (d) and EXAFS spectra (e) of CoPc/CNHs-3, CoPc and Co foil references. (f) Fitted Fourier-transformed EXAFS spectra in R space for CoPc/CNHs-3 and CoPc. Wavelet-transformed EXAFS spectra of CoPc/CNHs-3 (g), CoPc (h), and Co foil (i).

Fig. 3. Electrocatalytic CO2RR performance in acid electrolyte. (a) FEs and jCO of CoPc/CNHs with different Co contents. FEs and total current densities over CoPc/CNHs-3 in 1 mol L-1 KCl (pH = 1) (b) and 1 mol L-1 KCl (pH = 0.5) (d) catholyte. (c) TOF of CO production for CoPc/CNHs-3 and CoPc in 1 mol L-1 KCl (pH = 1) catholyte. The TOF is calculated based on the total number of Co atoms in the catalyst as determined by ICP-OES. (e) FEs of products and total current densities over CoPc/CNTs in 1 mol L-1 KCl (pH = 0.5) catholyte. (f) FEs and jCO of CoPc/CNHs-3 and CoPc/CNTs with electrolyte pH from 7 to 0.5. (g) CO2RR durability of CoPc/CNHs-3 at -1.4 V vs. RHE and the corresponding FECO and FEH2 evolution with time in 1 M KCl (pH = 1) catholyte. (h) Comparison of CO product performance in this study with values reported for other catalysts. The error bars represent the standard deviation of three independent measurements.

Fig. 4. Effect of restricted proton transfer and reaction kinetics measurements of CO2RR. (a) CVs of CoPc/CNHs-3 and CoPc/CNTs electrodes in Ar-saturated 0.5 mol L-1 H2SO4 with a scan rate of 100 mV s-1. LSV curves of CoPc/CNHs-3 (b) and CoPc/CNTs (d) on RDE in Ar-saturated 0.1 mol L-1 K2SO4 (pH = 2.5) with different rotation rates. Linear fitting plots based on Koutecky-Levich equation for CoPc/CNHs-3 (c) and CoPc/CNTs (e) catalysts. Potential-dependent in-situ Nyquist plots of CoPc/CNHs-3 (f) and CoPc/CNTs (g) catalysts. Potential-dependent in-situ Bode phase plots of CoPc/CNHs-3 (h) and CoPc/CNTs (i) catalysts.

Fig. 5. In-situ spectroscopic investigation for intermediates detection. In-situ ATR-SEIRAS spectra on CoPc/CNHs-3 (a), CoPc/CNTs (b), and CoPc (c) at different potentials. Band intensity of key intermediates CO32- (d), *COOH (e), and *CO (f) formed on surface of CoPc/CNHs-3, CoPc/CNTs, CoPc, and CNHs catalysts.

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Restricting proton transfer via carbon nanohorn-supported monomolecular cobalt phthalocyanine enhances CO₂-to-CO electrocatalysis in acidic media

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