An official website of the United States government
Alkaline fuel cells enable the use of earth-abundant elements to replace Pt but are hindered by the sluggish kinetics of the hydrogen oxidation reaction (HOR) in alkaline media. Precious metal–free HOR electrocatalysts need to overcome two major challenges: their low intrinsic activity from too strong a hydrogen-binding energy and poor durability due to rapid passivation from metal oxide formation. Here, we designed a Ni-based electrocatalyst with a 2-nm nitrogen-doped carbon shell (Ni@CN x ) that serves as a protection layer and significantly enhances HOR kinetics. A Ni@CN x anode, paired with a Co−Mn spinel cathode, exhibited a record peak power density of over 200 mW/cm 2 in a completely precious metal–free alkaline membrane fuel cell. Ni@CN x exhibited superior durability when compared to a Ni nanoparticle catalyst due to the enhanced oxidation resistance provided by the CN x layer. Density functional theory calculations suggest that graphitic carbon layers on the surface of the Ni nanoparticles lower the H binding energy to Ni, bringing it closer to the previously predicted value for optimal HOR activity, and single Ni atoms anchored to pyridinic or pyrrolic N defects of graphene can serve as the HOR active sites. The strategy described here marks a milestone in electrocatalyst design for low-cost hydrogen fuel cells and other energy technologies with completely precious metal–free electrocatalysts.
more »
« less
This content will become publicly available on April 9, 2026
Reorganizing the Pt Surface Water Structure for Highly Efficient Alkaline Hydrogen Oxidation Reaction
Thehydrogenoxidationreaction(HOR)inalkalineelectrolytesexhibitsmarkedlyslowerkineticsthanthatinacidic electrolytes.Thisposesacriticalchallengeforalkalineexchangemembranefuelcells(AEMFCs).Theslowerkineticsinalkaline electrolytesisoftenattributedtothemoresluggishVolmerstep(hydrogendesorption).IthasbeenshownthatthealkalineHOR activityonthePtsurfacecanbeconsiderablyenhancedbythepresenceofoxophilictransitionmetals(TMs)andsurface-adsorbed hydroxylgroupsonTMs(TM−OHad),althoughtheexactroleofTM−OHadremainsatopicofactivedebates.Herein,usingsingle- atomRh-tailoredPtnanowiresasamodelsystem,wedemonstratethathydroxylgroupsadsorbedontheRhsites(Rh−OHad)can profoundly reorganize the Pt surface water structure to deliver a record-setting alkaline HOR performance. In situ surface characterizations,togetherwiththeoreticalstudies,revealthatsurfaceRh−OHadcouldpromotetheoxygen-downwater(H2O↓)that favorsmorehydrogenbondwithPtsurfaceadsorbedhydrogen(H2O↓···Had-Pt)thanthehydrogen-downwater(OH2↓).TheH2O↓ furtherservesasthebridgetofacilitatetheformationofanenergeticallyfavorablesix-membered-ringtransitionstructurewith neighboringPt−Had andRh−OHad,thusreducingtheVolmerstepactivationenergyandboostingHORkinetics.
more »
« less
- Award ID(s):
- 2404462
- PAR ID:
- 10585261
- Editor(s):
- Carreira, Erick
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Journal of the American Chemical Society
- Volume:
- 147
- Issue:
- 14
- ISSN:
- 0002-7863
- Page Range / eLocation ID:
- 12162 to 12169
- Subject(s) / Keyword(s):
- Catalysts, Hydrogen oxidation reaction, Single atom, Water layer
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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.more » « less
-
Transition metal carbides are attractive, low-cost alternatives to Pt group metals, exhibiting multifunctional acidic, basic, and metallic sites for catalysis. Their widespread applications are often impeded by a high surface affinity for oxygen, which blocks catalytic sites. However, recent reports indicate that the α-MoC phase is a stable and effective cocatalyst for reactions in oxidative or aqueous environments. In this work, we elucidate the factors affecting the stability and catalytic activity of α-MoC under mild electrooxidation conditions (0–0.8 V SHE) using density functional theory calculations, kinetics-informed surface Pourbaix diagram analysis, electronic structure analysis, and cyclic voltammetry. Both computational and experimental data indicate that α-MoC is significantly more resistant to electrooxidation by H2O than β-Mo2C. This higher stability is attributed to structural and kinetic factors, as the Mo-terminated α-MoC surface disfavors substitutional oxidation of partially exposed, less oxophilic C* atoms by hindering CO/CO2 removal. The α-MoC surface exposes H2O-protected [MoC2O2] and [MoC(CO)O2] oxycarbidic motifs available for catalysis in a wide potential window. At higher potentials, they convert to unstable [Mo(CO)2O2], resulting in material degradation. Using formic acid as a probe molecule, we obtain evidence for Pt-like O*-mediated O–H and C–H bond activation pathways. The largest kinetic barrier, observed for the C–H bond activation, correlates with the hydrogen affinity of the site in the order O*/Mofcc > O*/Ctop > O*/Motop. To mitigate the site-blocking effect of surface-bound H2O and bidentate formate, doping with Pt was investigated computationally to make the surface less oxophilic and more carbophilic, indicating a possible design strategy toward more active and selective carbide electrocatalysts.more » « less
-
Abstract The Tucana–Horologium association (Tuc-Hor) is a 40 Myr old moving group in the southern sky. In this work, we measure the rotation periods of 313 Tuc-Hor objects with TESS light curves derived from TESS full-frame images and membership lists driven by Gaia EDR3 kinematics and known youth indicators. We recover a period for 81.4% of the sample and report 255 rotation periods for Tuc-Hor objects. From these objects we identify 11 candidate binaries based on multiple periodic signals or outlier Gaia DR2 and EDR3 renormalized unit weight error values. We also identify three new complex rotators (rapidly rotating M dwarf objects with intricate light-curve morphology) within our sample. Along with the six previously known complex rotators that belong to Tuc-Hor, we compare their light-curve morphology between TESS Cycle 1 and Cycle 3 and find that they change substantially. Furthermore, we provide context for the entire Tuc-Hor rotation sample by describing the rotation period distributions alongside other youth indicators such as Hα and Li equivalent width, as well as near-ultraviolet and X-ray flux. We find that measuring rotation periods with TESS is a fast and effective means to confirm members in young moving groups.more » « less
-
La0.7Sr0.2Ni0.2Fe0.8O3 (LSNF), having thermochemical stability, superior ionic and electronic conductivity, and structural flexibility, was investigated as a cathode in SOECs. Exsolution of nanoparticles by reduction of LSNF at elevated temperatures can modulate the characteristics of adsorption, electron transfer, and oxidation states of catalytically active atoms, consequently improving the electrocatalytic activity. The exsolution of NiFe and La2NiO4 nanoparticles to the surface of LSNF under reducing atmosphere (5% H2/N2) was verified at various temperatures (500–800 °C) by IFFT from ETEM, TPR and in situ XRD. The exsolved nanoparticles obtained uniform size distribution (4.2–9.2 nm) and dispersion (1.31 to 0.61 × 104 particle per μm2) depending on the reduction temperature (700–800 °C) and time (0–10 h). The reoxidation of the reduced LSNF (Red-LSNF) was verified by the XRD patterns, indicative of its redox ability, which allows for redistribution of the nanoparticles between the surface and the bulk. TPD-DRIFTS analysis demonstrated that Red-LSNF had superior H2O and CO2 adsorption behavior as compared to unreduced LSNF, which we attributed to the abundance of oxygen vacancy sites and the exsolved NiFe and La2NiO4 nanoparticles. After the reduction of LSNF, the decreases in the oxidation states of the catalytically active ions, Fe and Ni, were characterized on the surface by XPS as well as in the bulk by XANES. The electrochemical performance of the Red-LSNF cell was superior to that of the LSNF cell for electrolysis of H2O, CO2, and H2O/CO2.more » « less
