Bifunctional oxygen catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with high activities and low‐cost are of prime importance and challenging in the development of fuel cells and rechargeable metal–air batteries. This study reports a porous carbon nanomaterial loaded with cobalt nanoparticles (Co@NC‐
Oxygen evolution reaction (OER) is of great significance for hydrogen production via water electrolysis, which, however, demands development of highly active, durable, and cost‐effective electrocatalysts in order to stride into a renewable energy era. Herein, highly efficient and long‐term durable OER by coupling B and P into an amorphous porous NiFe‐based electrocatalyst is reported, which possesses an amorphous porous metallic bulk structure and high corrosion resistance, and overcomes the issues associated with currently used catalyst nanomaterials. The PB codoping in the activated NiFePB (a‐NiFePB) delocalizes both Fe and Ni at Fermi energy level and enhances p–d hybridization as simulated by density functional theory calculations. The harmonized electronic structure and unique porous framework of the a‐NiFePB consequently improve the OER activity. The activated NiFePB thus exhibits an extraordinarily low overpotential of 197 mV for harvesting 10 mA cm−2OER current density and 233 mV for reaching 100 mA cm−2under chronopotentiometry condition, with the Tafel slope harmoniously conforming to 34 mV dec−1. Impressive long‐term stability of this new catalyst is evidenced by only limited activity decay after 1400 h operation at 100 mA cm−2. This work strategically directs a way for heading up a promising energy conversion alternative.
more » « less- Award ID(s):
- 1665265
- NSF-PAR ID:
- 10372145
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 15
- Issue:
- 28
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract x /y ) derived from pyrolysis of a Co/Zn bimetallic zeolitic imidazolite framework, which exhibits incredibly high activity as bifunctional oxygen catalysts. For instance, the optimal catalyst of Co@NC‐3/1 has the interconnected framework structure between porous carbon and embedded carbon nanotubes, which shows the superb ORR activity with onset potential of ≈1.15 V and half‐wave potential of ≈0.93 V. Moreover, it presents high OER activity that can be further enhanced to over commercial RuO2by P‐doped with overpotentials of 1.57 V versus reversible hydrogen electrode at 10 mA cm−2and long‐term stability for 2000 circles and a Tafel slope of 85 mV dec−1. Significantly, the nanomaterial demonstrates better catalytic performance and durability than Pt/C for ORR and commercial RuO2and IrO2for OER. These findings suggest the importance of a synergistic effect of graphitic carbon, nanotubes, exposed Co–Nx active sites, and interconnected framework structure of various carbons for bifunctional oxygen electrocatalysts. -
more » « less
Abstract The main drawbacks of today's state‐of‐the‐art lithium–air (Li–air) batteries are their low energy efficiency and limited cycle life due to the lack of earth‐abundant cathode catalysts that can drive both oxygen reduction and evolution reactions (ORR and OER) at high rates at thermodynamic potentials. Here, inexpensive trimolybdenum phosphide (Mo3P) nanoparticles with an exceptional activity—ORR and OER current densities of 7.21 and 6.85 mA cm−2at 2.0 and 4.2 V versus Li/Li+, respectively—in an oxygen‐saturated non‐aqueous electrolyte are reported. The Tafel plots indicate remarkably low charge transfer resistance—Tafel slopes of 35 and 38 mV dec−1for ORR and OER, respectively—resulting in the lowest ORR overpotential of 4.0 mV and OER overpotential of 5.1 mV reported to date. Using this catalyst, a Li–air battery cell with low discharge and charge overpotentials of 80 and 270 mV, respectively, and high energy efficiency of 90.2% in the first cycle is demonstrated. A long cycle life of 1200 is also achieved for this cell. Density functional theory calculations of ORR and OER on Mo3P (110) reveal that an oxide overlayer formed on the surface gives rise to the observed high ORR and OER electrocatalytic activity and small discharge/charge overpotentials.
-
null (Ed.)Iridium oxide (IrO 2 ) is one of the best known electrocatalysts for the oxygen evolution reaction (OER) taking place in a strongly acidic solution. IrO 2 nanocatalysts with high activity as well as long-term catalytic stability, particularly at high current densities, are highly desirable for proton exchange membrane water electrolysis (PEM-WE). Here, we report a simple and cost-effective strategy for depositing ultrafine oxygen-defective IrO x nanoclusters (1–2 nm) on a high-surface-area, acid-stable titanium current collector (H-Ti@IrO x ), through a repeated impregnation–annealing process. The high catalytically active surface area resulting from the small size of IrO x and the preferable electronic structure originating from the presence of oxygen defects enable the outstanding OER performance of H-Ti@IrO x , with low overpotentials of 277 and 336 mV to deliver 10 and 200 mA cm −2 in 0.5 M H 2 SO 4 . Moreover, H-Ti@IrO x also shows an intrinsic specific activity of 0.04 mA cm catalyst −2 and superior mass activity of 1500 A g Ir −1 at an overpotential of 350 mV. Comprehensive experimental studies and density functional theory calculations confirm the important role of oxygen defects in the enhanced OER performance. Remarkably, H-Ti@IrO x can continuously catalyze the OER in 0.5 M H 2 SO 4 at 200 mA cm −2 for 130 hours with minimal degradation, and with a higher IrO x loading, it can sustain at such a high current density for over 500 hours without significant performance decay, holding substantial promise for use in PEM-WE.more » « less
-
more » « less
Abstract Designing cost‐efffective electrocatalysts for the oxygen evolution reaction (OER) holds significant importance in the progression of clean energy generation and efficient energy storage technologies, such as water splitting and rechargeable metal–air batteries. In this work, an OER electrocatalyst is developed using Ni and Fe precursors in combination with different proportions of graphene oxide. The catalyst synthesis involved a rapid reduction process, facilitated by adding sodium borohydride, which successfully formed NiFe nanoparticle nests on graphene support (NiFe NNG). The incorporation of graphene support enhances the catalytic activity, electron transferability, and electrical conductivity of the NiFe‐based catalyst. The NiFe NNG catalyst exhibits outstanding performance, characterized by a low overpotential of 292.3 mV and a Tafel slope of 48 mV dec−1, achieved at a current density of 10 mA cm−2. Moreover, the catalyst exhibits remarkable stability over extended durations. The OER performance of NiFe NNG is on par with that of commercial IrO2in alkaline media. Such superb OER catalytic performance can be attributed to the synergistic effect between the NiFe nanoparticle nests and graphene, which arises from their large surface area and outstanding intrinsic catalytic activity. The excellent electrochemical properties of NiFe NNG hold great promise for further applications in energy storage and conversion devices.
-
null (Ed.)Electrochemical water splitting is one of the most promising approaches for sustainable energy conversion and storage toward a future hydrogen society. This demands durable and affordable electrocatalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In this study, we report the preparation of uniform Ni–P–O, Ni–S–O, and Ni–S–P–O electrocatalytic films on nickel foam (NF) substrates via flow cell-assisted electrodeposition. Remarkably, electrodeposition onto 12 cm 2 substrates was optimized by strategically varying critical parameters. The high quality and reproducibility of the materials is attributed to the use of a 3D-printed flow cell with a tailored design. Then, the as-fabricated electrodes were tested for overall water splitting in the same flow cell under alkaline conditions. The best-performing sample, NiSP/NF, required relatively low overpotentials of 93 mV for the HER and 259 mV for the OER to produce a current density of 10 mA cm −2 . Importantly, the electrodeposited films underwent oxidation into amorphous nickel (oxy)hydroxides and oxidized S and P species, improving both HER and OER performance. The superior electrocatalytic performance of the Ni–S–P–O films originates from the unique reconstruction process during the HER/OER. Furthermore, the overall water splitting test using the NiSP/NF couple required a low cell voltage of only 1.85 V to deliver a current density of 100 mA cm −2 . Overall, we demonstrate that high-quality electrocatalysts can be obtained using a simple and reproducible electrodeposition method in a robust 3D-printed flow cell.more » « less
