No abstract

PtM (M = transition metals) nanomaterials have been recognized as promising catalysts for the oxygen reduction reaction (ORR) in fuel cells, with a much higher performance than pure Pt. However, the insufficient durability issue of PtM is often raised because of the fast dissolution of M in acid, impeding their commercialization. Herein, we report on a Ketjenblack (KB)-supported, nitrogen (N)-doped intermetallic PtNiN (Int-PtNiN/KB) catalyst that exhibits remarkably enhanced ORR activity and stability in an acidic electrolyte, superior to those of disordered PtNi/KB, disordered PtNiN/KB, and commercial Pt/C. The experimental results show that Int-PtNiN/KB has a distinctive ordering structure of alternating Ni4–N and Pt planes; we attribute the origin of the superior stability of this catalyst to the combined effect of the Ni4–N formation and the unique intermetallic structure, which effectively precludes Ni dissolution from the core. The density functional theory calculations suggest that the tensile strain introduced by the formation of an intermetallic phase and N-doping optimizes the binding of oxygenated species on the Pt surface and enable highly efficient electron transfer, leading to the enhanced ORR performance. This study offers an appropriate route for further enhancing both the activity and durability of PtM catalysts through a facile synthesis method by annealing in an NH3 gas under appropriate conditions.

Bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are very crucial for converting water into clean fuel through overall water splitting. Here, we report on a bifunctional catalyst based on Ir-doped NiV layered double hydroxide with Ir−O−V catalytic groups on which water dissociation, HER, and OER occur on Ir, bridge O, and V atoms, respectively. Interestingly, the dopant Ir ions were found to play a triple role: (i) serve as catalytic sites for water dissociation, (ii) reduce charge density on adjacent bridge oxygen, thus facilitating HER there, and (iii) increase charge density on V ions, which in turn boosts OER. As a result, the catalyst achieves an ultralow applied voltage for overall water splitting (1.49 V @ 10 mA cm −2 ) and beats the noble metallic couple Pt/C and Ir/C with its value of 1.60 V @ 10 mA cm −2 .

The surface of an electrocatalyst undergoes dynamic chemical and structural transformations under electrochemical operating conditions. There is a dynamic exchange of metal cations between the electrocatalyst and electrolyte. Understanding how iron in the electrolyte gets incorporated in the nickel hydroxide electrocatalyst is critical for pinpointing the roles of Fe during water oxidation. Here, we report that iron incorporation and oxygen evolution reaction (OER) are highly coupled, especially at high working potentials. The iron incorporation rate is much higher at OER potentials than that at the OER dormant state (low potentials). At OER potentials, iron incorporation favors electrochemically more reactive edge sites, as visualized by synchrotron X-ray fluorescence microscopy. Using X-ray absorption spectroscopy and density functional theory calculations, we show that Fe incorporation can suppress the oxidation of Ni and enhance the Ni reducibility, leading to improved OER catalytic activity. Our findings provide a holistic approach to understanding and tailoring Fe incorporation dynamics across the electrocatalyst–electrolyte interface, thus controlling catalytic processes.

It is highly desirable to develop all-pH-compatible hydrogen evolution reaction (HER) electrocatalysts that can be used universally in a variety of different electrolyzers and operated in different pH conditions, i.e., acid, alkaline, microbial, chlor-alkali, etc. So far, two-dimensional layered MoS2 and Mo-based carbon materials have been regarded as promising pH-universal HER electrocatalysts. 2H-MoS2 as a naturally occurring and thermodynamically favorable phase, yet still suffers from poor HER activity in neutral and alkaline electrolytes. Herein, a hybrid electrocatalyst, i.e., 2H-MoS2/N-doped mesoporous graphene, rich in interfacial Mo–pyridinic N coordination is fabricated. The optimized hybrid catalyst delivers long-term durability and outstanding HER activity with overpotentials of 110, 145, and 142 mV at 10 mA cm–2 in acidic, alkaline, and phosphate buffered solutions (PBS) media, respectively, outperforming most of the previously reported MoS2-based catalysts. Theoretical and experimental results demonstrate that the interfacial pyridinic N has a higher tendency to bond with Mo atoms than pyrrolic and graphitic N, and the edge-Mo coordinated with pyridinic N could serve as HER active sites. DFT calculations further reveal that Mo–pyridinic N coordination modifies the charge density of edge-Mo, in turn optimizing the hydrogen absorption energy and facilitating water dissociation, and thereby significantly promoting the intrinsic catalytic activity for the pH-universal HER process.