RESUMEN
The oxygen evolution reaction (OER) plays a vital role in renewable energy technologies, including in fuel cells, metal-air batteries, and water splitting; however, the currently available catalysts still suffer from unsatisfactory performance due to the sluggish OER kinetics. Herein, we developed a new catalyst with high efficiency in which the dynamic exchange mechanism of active Fe sites in the OER was regulated by crystal plane engineering and pore structure design. High-density nanoholes were created on cobalt hydroxide as the catalyst host, and then Fe species were filled inside the nanoholes. During the OER, the dynamic Fe was selectively and strongly adsorbed by the (101Ì 0) sites on the nanohole walls rather than the (0001) basal plane, and at the same time the space-confining effect of the nanohole slowed down the Fe diffusion from catalyst to electrolyte. As a result, a local high-flux Fe dynamic equilibrium inside the nanoholes for OER was achieved, as demonstrated by the Fe57 isotope labeled mass spectrometry, thereby delivering a high OER activity. The catalyst showed a remarkably low overpotential of 228 mV at a current density of 10 mA cm-2, which is among the best cobalt-based catalysts reported so far. This special protection strategy for Fe also greatly improved the catalytic stability, reducing the Fe leaching amount by 2 orders of magnitude compared with the pure Fe hydroxide catalyst and thus delivering a long-term stability of 130 h. An assembled Zn-air battery was stably cycled for 170 h with a low discharge/charge voltage difference of 0.72 V.
RESUMEN
Owing to sluggish reaction kinetics and high potential, oxygen evolution reaction (OER) electrocatalysts face a trade-off between activity and stability. Herein, an innovative topological strategy is presented for preparing 2D multimetallic (oxy)hydroxide, including ternary CoFeZn, quaternary CoFeMnZn, and high-entropy CoFeMnCuZn. The key to the synthesis lies in using Ca-rich brownmillerite oxide as a precursor, which possesses inherent structural flexibility enabling tailored elemental adjustments and topologically transforms from a point-shared structure of metal-oxygen octahedrons into an edge-shared structure under alkaline conditions. The presence of Zn in the catalysts causes a shift in the center of the O2p band toward the Fermi level, resulting in more Co4+ species, which drive holes into oxygen ligands to promote intramolecular oxygen coupling. The triggered lattice oxidation mechanism is identified by detecting peroxo-like (O2 2-) negative species using tetramethylammonium chemical probe, along with 18O isotope labeling experiments. As a result, the catalyst demonstrates an overpotential of 267 mV at 10 mA cm-2, ranking it among the top-performing non-Ni-based catalysts. Importantly, the catalysts also show high Fe-leaching resistance during OER compared to conventional NiFe and CoFe hydroxides/(oxy)hydroxides. The assembled zinc-air battery enables stable operation for over 225 h at a low charging voltage of 1.93 V.
RESUMEN
The oxygen evolution reaction (OER) is a key reaction in water splitting and metal-air batteries, and transition metal hydroxides have demonstrated the most electrocatalytic efficiency. Making the hydroxides thinner for more surface commonly fails to increase the active site number, because the real active sites are the edges. Up to now, the overpotentials of most state-of-the-art OER electrocatalysts at a current density of 10 mA cm-2 (η10 ) are still larger than 200 mV. Herein, a novel design of mesoporous single crystal (MSC) with an Fe-rich skin to boost the OER is shown. The edges around the mesopores provide lots of real active sites and the Fe modification on these sites further improves the intrinsic activity. As a result, an ultralow η10 of 185 mV is achieved, and the turnover frequency based on Fe atoms is as high as 16.9 s-1 at an overpotential of 350 mV. Moreover, the catalyst has an excellent catalytic stability, indicated by a negligible current drop after 10â¯000 cyclic voltammetry cycles. The catalyst enables Zn-air batteries to run stably over 270 h with a low charge voltage of 1.89 V. This work shows that MSC materials can provide new opportunities for the design of electrocatalysts.