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Metal complexes hybridized with conductive supports are desirable as high-performance catalysts for CO2 electroreduction, while the delicate molecular design to improve both the intrinsic activity of complex and the molecule-support interactions still remains challenging. We here employ a conjugation-tuning strategy by comparison between Ni(ii) octabutoxyphthalocyanine and Ni(ii) octabutoxynaphthalocyanine on multi-walled carbon nanotubes (NiPc-B@CNT and NiNc-B@CNT) in aqueous electrocatalytic CO2 reduction, respectively. In contrast to the conventional promotive effects from extended conjugation, the impaired conjugation in the Ni(ii) macrocycles unusually boosts both activity and molecule-support affinity. These merits can be attributed to the favored electronic effects and the higher flexibility of long alkyl chains both arising from the absent extended benzene ring in NiPc-B. Consequently, NiPc-B@CNT exhibits much higher faradaic efficiencies for CO production (FECO ≥ 94% among −0.79 to −1.09 V vs. RHE) than NiNc-B@CNT (FECO < 20%) in an H-cell configuration. The use of a gas-diffusion electrode further raises the electrocatalytic performances of NiPc-B@CNT under 1 atm CO2 (FECO ≈ 100% at −0.15 A cm−2) or simulated flue gas (10% CO2, FECO ≈ 80% at −0.1 A cm−2), respectively. © 2023 The Royal Society of Chemistry.

Current concerns on material-design induced mass transfer processes during small molecule electrocatalysis are on the ones assisted by external forced convection generally via electrode rotating, demonstrating the intrinsic activity of catalysts. Of note is that, in practical battery configurations, there is no the forced convection around electrode micro-environments. Therefore, the establishment of effective strategies in tuning the inherent mass transfer process, the one with no assistance by external forced convection, is also greatly significant, but rarely reported, retarding further advances. Herein, a size-induced inherent mass-transfer strategy is scrupulously established through designed kinetic investigations and also controllable construction of uniform Co, N co-doped carbon materials with a wide range of tunable particle sizes from 10 nm to 2 μm. The catalysts are synthesized by a pyrolysis of zeolitic imidazolate framework (ZIF) 67@ZIF-8, in which the wrapped shell layer avoids evident metal aggregations, and also contributes to rich porous environments after carbonizations. It is unclosed that particle size has a considerable effect on inherent mass transfer processes, even for the porous carbon catalysts. A particle size at around 700 nm is revealed to be most favorable for the inherent mass transfer process within the probed range, revealed by the smallest difference of Tafel slopes obtained with no electrode rotation and with infinite rotation speed. The latter is achieved via extrapolating rotation speeds to infinity in the Koutecký-Levich plots, by which the external mass transfer limitation can be completely eliminated. Contributed by the great inherent mass transfer process, the catalyst with a particle size of around 700 nm exhibits an impressive ORR activity in both three-electrode systems and zinc-air batteries. This work not only establishes a novel strategy in tuning inherent mass transfer process for small molecule electrocatalysis, more, QC 20210319

Pt based materials are the most efficient electrocatalysts for the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in fuel cells. Maximizing the utilization of Pt based materials by modulating their morphologies to expose more active sites is a fundamental objective for the practical application of fuel cells. Herein, we report a new class of hierarchically skeletal Pt-Ni nanocrystals (HSNs) with a multi-layered structure, prepared by an inorganic acid-induced solvothermal method. The addition of H2SO4 to the synthetic protocol provides a critical trigger for the successful growth of Pt-Ni nanocrystals with the desired structure. The Pt-Ni HSNs synthesized by this method exhibit enhanced mass activity of 1.25 A mgpt−1 at 0.9 V (versus the reversible hydrogen electrode) towards ORR in 0.1-M HClO4, which is superior to that of Pt-Ni multi-branched nanocrystals obtained by the same method in the absence of inorganic acid; it is additionally 8.9-fold higher than that of the commercial Pt/C catalyst. Meanwhile, it displays enhanced stability, with only 21.6% mass activity loss after 10,000 cycles (0.6–1.0 V) for ORR. Furthermore, the Pt-Ni HSNs show enhanced activity and anti-toxic ability in CO for MOR. The superb activity of the Pt-Ni HSNs for ORR and MOR is fully attributed to an extensively exposed electrochemical surface area and high intrinsic activity, induced by strain effects, provided by the unique hierarchically skeletal alloy structure. The novel open and hierarchical structure of Pt-Ni alloy provides a promising approach for significant improvements of the activity of Pt based alloy electrocatalysts. © 2021 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences.