The sluggish hydrogen oxidation reaction (HOR) under alkaline conditions has hindered the commercialization of hydroxide‐exchange membrane hydrogen fuel cells. A low‐cost Ni/NiO/C catalyst with abundant Ni/NiO interfacial sites was developed as a competent HOR electrocatalyst in alkaline media. Ni/NiO/C exhibits an HOR activity one order of magnitude higher than that of its parent Ni/C counterpart. Moreover, Ni/NiO/C also shows better stability and CO tolerance than commercial Pt/C in alkaline media, which renders it a very promising HOR electrocatalyst for hydrogen fuel cell applications. Density functional theory (DFT) calculations were also performed to shed light on the enhanced HOR performance of Ni/NiO/C; the DFT results indicate that both hydrogen and hydroxide achieve optimal binding energies at the Ni/NiO interface, resulting from the balanced electronic and oxophilic effects at the Ni/NiO interface.
Alkaline hydrogen evolution reaction (HER), consisted of Volmer and Heyrovsky/Tafel steps, requires extra energy for water dissociation, leading to more sluggish kinetics than acidic HER. Despite the advances in electrocatalysts, how to combine active sites to synergistically promote both steps and understand the underlying mechanism remain largely unexplored. Here, DFT calculations predict that NiO accelerates Volmer step while metallic Ni facilitates Heyrovsky/Tafel step. A facile strategy is thus developed to control Ni/NiO heterosurfaces in uniform and well-dispersed Ni-based nanocrystals, targeting both reaction steps synergistically. By systematically modulating the surface composition, we find that steering the elementary steps through tuning the Ni/NiO ratio can significantly enhance alkaline HER activity and Ni/NiO nanocrystals with a Ni/NiO ratio of 23.7% deliver the best activity, outperforming other state-of-the-art analogues. The results suggest that integrating bicomponent active sites for elementary steps is effective for promoting alkaline HER, but they have to be balanced.
more » « less- Award ID(s):
- 1828019
- NSF-PAR ID:
- 10119541
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- National Science Review
- ISSN:
- 2095-5138
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The sluggish hydrogen oxidation reaction (HOR) under alkaline conditions has hindered the commercialization of hydroxide‐exchange membrane hydrogen fuel cells. A low‐cost Ni/NiO/C catalyst with abundant Ni/NiO interfacial sites was developed as a competent HOR electrocatalyst in alkaline media. Ni/NiO/C exhibits an HOR activity one order of magnitude higher than that of its parent Ni/C counterpart. Moreover, Ni/NiO/C also shows better stability and CO tolerance than commercial Pt/C in alkaline media, which renders it a very promising HOR electrocatalyst for hydrogen fuel cell applications. Density functional theory (DFT) calculations were also performed to shed light on the enhanced HOR performance of Ni/NiO/C; the DFT results indicate that both hydrogen and hydroxide achieve optimal binding energies at the Ni/NiO interface, resulting from the balanced electronic and oxophilic effects at the Ni/NiO interface.
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Abstract Nickel sulfide (Ni3S2) is a promising hydrogen evolution reaction (HER) catalyst by virtue of its metallic electrical conductivity and excellent stability in alkaline medium. However, the reported catalytic activities for Ni3S2are still relatively low. Herein, an effective strategy to boost the H adsorption capability and HER performance of Ni3S2through nitrogen (N) doping is demonstrated. N‐doped Ni3S2nanosheets achieve a fairly low overpotential of 155 mV at 10 mA cm−2and an excellent exchange current density of 0.42 mA cm−2in 1.0
m KOH electrolyte. The mass activity of 16.9 mA mg−1and turnover frequency of 2.4 s−1obtained at 155 mV are significantly higher than the values reported for other Ni3S2‐based HER catalysts, and comparable to the performance of best HER catalysts in alkaline medium. These experimental data together with theoretical analysis suggest that the outstanding catalytic activity of N‐doped Ni3S2is due to the enriched active sites with favorable H adsorption free energy. The activity in the Ni3S2is highly correlated with the coordination number of the surface S atoms and the charge depletion of neighbor Ni atoms. These new findings provide important guidance for future experimental design and synthesis of optimal HER catalysts. -
null (Ed.)This paper reports a highly active and stable nonprecious metal electrocatalyst based on bimetallic nanoscale nickel molybdenum nitride developed for the hydrogen evolution reaction (HER). A composite of 7 nm Ni 2 Mo 3 N nanoparticles grown on nickel foam (Ni 2 Mo 3 N/NF) was prepared through a simple and economical synthetic method involving one-step annealing of Ni foam, MoCl 5 , and urea without a Ni precursor. The Ni 2 Mo 3 N/NF exhibits high activity with low overpotential ( η 10 of 21.3 mV and η 100 of 123.8 mV) and excellent stability for the HER, achieving one of the best performances among state-of-the-art transition metal nitride based catalysts in alkaline media. Supporting density functional theory (DFT) calculations indicate that N sites in Ni 2 Mo 3 N with a N–Mo coordination number of four have a hydrogen adsorption energy close to that of Pt and hence may be responsible for the enhanced HER performance.more » « less
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Abstract Several transition‐metal oxides and hydroxides based on earth‐abundant elements, such as Fe, Ni, and Co, have emerged as a new generation of oxygen evolution reaction (OER) catalysts due to their low cost, favorable activity, and multifunctional behavior. However, the relatively complicated surface structuring methods, high Tafel slope, and low stability hinder their practical applications to replace the conventional Ir‐ and Ru‐based catalysts. Herein, a strategy to construct hierarchically architected mixed oxides on conductive substrates (e.g., ITO and Ni foam) via a nanosheet (NS) deposition and subsequent bidirectional nanomodification approach, with metal salts in an aprotic polar solvent (e.g., acetone) as the primary modifying reactants is reported. This strategy is used to prepare NiO‐based NSs with nanopores, nanobranches, or a combination of both, containing up to four transition metal elements. Record‐low Tafel slope (22.3 mV·dec−1, ≈lowest possible by computational predictions) and week‐long continuous operation durability are achieved by FeMnNi‐O NSs supported on Ni foams. Taken together, properly designed hierarchical mixed oxide electrodes may provide a cost‐effective route to generating high, reliable, and stable OER catalytic activities, paving the way for both new electrocatalyst design and practical water‐splitting devices.
