Sensitivity of Gas-Evolving Electrocatalysis to the Catalyst Microenvironment

Abstract

Many electrochemical reactions for the development of renewable energy technologies are gas-evolving reactions, where the electrocatalytic performance is susceptible to the wetting properties of the catalyst microenvironment. Here, using N2H4 electro-oxidation to N2 on carbon-supported Pt nanocatalysts as a model reaction, we controlled the microenvironment using oxygen-doped and fluorine-doped carbon supports to make it more hydrophilic and more hydrophobic, respectively, and elucidated the effect on the reaction kinetics. The electrode with oxygen-doped carbon showed a 123% higher activity than that with pristine carbon, benefiting from the increased wetting and exposure of Pt catalytic sites to the electrolyte. Counterintuitively, the electrode with fluorine-doped carbon also exhibited a 46% higher activity than that with pristine carbon, despite its lower wetting of Pt. We found that the hydrophobic microenvironment accelerated the surface diffusion, coalescence, and detachment of the generated N2 gas bubbles, which would otherwise block the Pt active sites from catalyzing the reaction.

In Situ Preparation of Polyamine-Derived Ru Cluster@N-Doped Porous Carbon Nanoplates for Hydrogen Evolution over Wide pH Ranges

“…The improvements in reaction kinetics may be ascribed to the strong interaction of Ru and the high graphitized carbon substrate. The ECSA value can be calculated using the double-layer capacitance ( C dl ) and Cu under the potential deposition method (Cu UPD), , where the C dl is determined to be linearly proportional to the number of active sites (Figures e and S13). After calculation from the equation of ECSA = C dl / C s (where the C s value is the specific capacitance of the electrode under 0.5 M H 2 SO 4 solution), the ECSA of Ru cluster@NCs is 30.70 m 2 g –1 , which was larger than that of commercial Pt/C (29.67 m 2 g –1 ), Ru(10%)@NCs (7.77 m 2 g –1 ), and Ru(1.5%)@NCs (6.76 m 2 g –1 ).…”

Hydrophilic or Hydrophobic? Optimizing the Catalyst Microenvironment for Gas‐Involving Electrocatalysis

“…According to the average fluctuation periods (Figure 4d), the Pt/C‐F‐800 electrode showed the shortest cycle or lifetime of the gas bubble dynamics, indicating that it took a shorter time for the bubbles to grow and reach the critical size due to a higher bubble growth rate. Our optical microscopy observations revealed that the hydrophobic microenvironment in the Pt/C‐F‐800 electrode resulted in a faster diffusion and coalescence of gas bubbles, [52] and thus accelerated the detachment of the generated gas bubbles and the recovery of Pt active sites. The faster gas bubble release could compensate the negative impact of the lower ECSA, so that the Pt/C‐F‐800 electrode still showed a higher current density than the Pt/C electrode (Figure 4a).…”

“…In our recent work, we used the electro-oxidation of N 2 H 4 to N 2 gas on carbon-supported Pt nanocatalyst as a model system to investigate the effect of microenvironment on the gasevolving reaction. [52] In contrast to previous studies, [29] we relied on the widely used electrode formulation with carbonsupported nanocatalyst, and tuned the microenvironment over a wide range of wetting conditions by doping of the carbon support (Vulcan XC-72 carbon black). Again, O-doping makes the carbon support more hydrophilic while F-doping makes it more hydrophobic.…”

“…By mixing the Pt/C nanoparticle catalyst and the carbon blacks with different doping levels, we prepared a series of electrodes with the same Pt nanocatalyst but distinct microenvironments over a wide range of hydrophilicity and hydrophobicity. The post‐reaction contact angles were measured to be 19.7°, 74.0°, and 143.6° for the Pt/C‐O‐12h, Pt/C, and Pt/C‐F‐800 electrodes, [52] which reflect their actual wetting states during electrochemical tests. The electrocatalytic performance for N 2 H 4 oxidation reaction was evaluated on these electrodes at 0.5 V vs RHE in H‐cell.…”

“…(d) Average fluctuation periods of the overpotential presented in (c). Adapted with permission from Ref [52]. Copyright 2023 American Chemical Society.…”