Platinum Nanostructure/Nitrogen‐Doped Carbon Hybrid: Enhancing its Base Media HER/HOR Activity through Bi‐functionality of the Catalyst

Abstract

The design and synthesis of an active catalyst for the hydrogen evolution reaction/hydrogen oxidation reaction (HER/HOR) are important for the development of hydrogen‐based renewable technologies. The synthesis of a hybrid of platinum nanostructures and nitrogen‐doped carbon [Pt‐(PtOx)‐NSs/C] for HER/HOR applications is reported herein. The HER activity of this Pt‐(PtOx)‐NSs/C catalyst is 4 and 6.5 times better than that of commercial Pt/C in acids and bases, respectively. The catalyst exhibits a current density of 10 mA cm−2 at overpotentials of 5 and 51 mV, with Tafel slopes of 29 and 64 mV dec−1 in 0.5 m H2SO4 and 0.5 m KOH. This catalyst also showed superior HOR activity at all pH values. The HER/HOR activity of Pt‐(PtOx)‐NSs/C and PtOx‐free Pt‐nanostructures on carbon (PtNSs/C) catalysts are comparable in acid. The presence of PtOx in Pt‐(PtOx)‐NSs/C makes this Pt catalyst more HER/HOR‐active in basic media. The activity of the Pt‐(PtOx)‐NSs/C catalyst is fivefold higher than that of the PtNSs/C catalyst in basic medium, although their activity is comparable in acid. The hydrogen‐binding energy and oxophilicity are two equivalent descriptors for HER/HOR in basic media. A bifunctional mechanism for the enhanced alkaline HER/HOR activity of the Pt‐(PtOx)‐NSs/C catalyst is proposed. In the bifunctional Pt‐(PtOx)‐NSs/C catalyst, PtOx provides an active site for OH− adsorption to form OHads, which reacts with hydrogen intermediate (Hads), present at neighbouring Pt sites to form H2O; this leads to enhancement of the HOR activity in basic medium. This work may provide an opportunity to develop catalysts for various renewable‐energy technologies.

Bimetallic nickel-molybdenum/tungsten nanoalloys for high-efficiency hydrogen oxidation catalysis in alkaline electrolytes

“…Figure 5b further shows lower CO-stripping peaks at 0.52 and 0.49 V for MoNi 4 and WNi 4 catalysts, whereas the freshly synthesized Ni exhibits negligible CO-stripping peak. Some prior works have ascribed the sluggish HOR kinetics on Pt to its weak OH ad binding in alkali 8,23,27 . Our CO-stripping results here suggest that the enhanced OHBE on MoNi 4 and WNi 4 could also be responsible for their high HOR energetics.…”

“…Unfortunately, the anode hydrogen oxidation reaction (HOR) activity on PGM catalysts (e.g., Pt, Ir, and Pd) is about two to three orders of magnitude slower in alkali than in acidic electrolytes 6,7 . This consequently causes higher PGM loadings at the anode that could largely offset the reduced cost from the use of PGM-free cathodes 8 . As a result, the development of durable PGM-free catalytic materials with high intrinsic HOR activity in alkali is important to the eventual success of HEMFC technology.…”

“…Moreover, alloying PGMs with other metals can enable performance enhancements resulting from the modified surface structures; typical examples include PtNi 13 , PtRu 14 , Pt-coated Cu 15 , body-centered cubic PdCu 9 , and others [16][17][18][19][20] . In the quest to understand why the HOR reactivity in alkaline media is significantly slower than that in acid on PGMs, there has been extensive debate over whether such sluggish HOR kinetics in alkali is determined by hydrogen binding energy (HBE) or OH binding energy (OHBE)/ oxophilicity 8,10,11,13,[21][22][23][24][25][26][27] . The lack of a conclusive mechanistic relevance has somewhat hampered success in designing betterperforming HOR catalysts from PGMs.…”

Hydrogen Oxidation Artifact During Platinum Oxide Reduction in Cyclic Voltammetry Analysis of Low-Loaded PEMFC Electrodes

“…The response of the low-loaded electrodes upon the potential increase is a direct decrease in the H 2X -related current at potentials > 0.5 V and a flattening of the current towards the upper potential limit of 1 V. In comparison, the current of the 400 μg/cm 2 electrode first increases and then drops after potentials above 0.7 V, but it does not level out at about 1 V. Higher potentials were avoided during these LSV measurements, as the scan rate of 1 mV/s would be inevitably accompanied with unnecessary dwell times at potentials critical for corrosion of the carbon support [10,36]. While some studies point towards a complete suppression of HOR on PtOx [44][45][46], a newer study presents an improved HOR and H 2 evolution reaction (HER) activity of synthesized Pt-(PtOx)-Nitrogen doped hybrid catalysts [47]. In a study by Iden et al [48], the authors correlate the decrease in H 2X limiting current density to the increase in mass transfer losses due to the loss in effective ECSA, when Pt sites are blocked by surface oxides at elevated potentials.…”

Structural and Electrochemical Properties of Nesting and Core/Shell Pt/TiO2 Spherical Particles Synthesized by Ultrasonic Spray Pyrolysis

“…With the exception of the sample synthesized ex-situ at 650 • C (Figure 6b), values of CV currents of all the other Pt/TiO 2 samples are below 5 µA. Additionally, hydrogen reduction/oxidation peaks of considerable currents [52] at around -0.2 V are clearly registered only for the 650 • C sample with 20 mass % Pt. None of the samples show hydrogen adsorption/desorption region typical for Pt, as seen for Pt black (Figure 6b).…”