Inherent mass transfer engineering of a Co, N co-doped carbon material towards oxygen reduction reaction

• 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 importantly, it provides a new dimension in kinetic investigations and oriented design of advanced energy materials.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Energiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Energy Engineering (hsv//eng)

Nyckelord

Co

N co-doped porous carbon

Electrocatalysis

Oxygen reduction reaction

Zn-air battery

Carbon

Carbonization

Catalysis

Catalyst activity

Electrodes

Electrolytic reduction

Forced convection

Molecules

Oxygen

Particle size

Porous materials

Tuning

Zinc air batteries

Advanced energy materials

External mass transfer

Intrinsic activities

Kinetic investigations

Mass transfer process

Three electrode-system

Transfer strategies

Zeolitic imidazolate frameworks

Mass transfer

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