ABSTRACT
Scarce and expensive iridium oxide is still the cornerstone catalyst of polymer-electrolyte membrane electrolyzers for green hydrogen production because of its exceptional stability under industrially relevant oxygen evolution reaction (OER) conditions. Earth-abundant transition metal oxides used for this task, however, show poor long-term stability. We demonstrate here the use of nitrogen-doped cobalt oxide as an effective iridium substitute. The catalyst exhibits a low overpotential of 240 mV at 10 mA cm-2 and negligible activity decay after 1000 h of operation in an alkaline electrolyte. Incorporation of nitrogen dopants not only triggers the OER mechanism switched from the traditional adsorbate evolution route to the lattice oxygen oxidation route but also achieves oxygen nonbonding (ONB) states as electron donors, thereby preventing structural destabilization. In a practical anion-exchange membrane water electrolyzer, this catalyst at anode delivers a current density of 1000 mA cm-2 at 1.78 V and an electrical efficiency of 47.8 kW-hours per kilogram hydrogen.
ABSTRACT
Interfacial metal-support interaction (MSI) significantly affects the dispersion of active metals on the surface of the catalyst support and impacts catalyst performance. Understanding MSI is crucial for developing highly active and stable catalysts with a low metal loading, particularly for noble metal catalysts. In this work, we synthesized LaRuxCr1-xO3 catalysts with low Ru loading (x = 0.005, 0.01, and 0.02) using the sol-gel self-combustion method. We found that all of the Ru atoms immediately above or below the metal-support interface are closely bonded to the perovskite LaCrO3 surface lattice through Ru-O bonds, enhancing the MSI via interfacial reaction and charge transfer mechanisms. We identified a variety of Ru species, including small 3D Ru nanoparticles, 2D dispersed Ru surface atoms, and even 0D Ru single atoms. These highly dispersed Ru species exhibit high activity and stability under dry reforming of methane (DRM) conditions. The LaRu0.01Cr0.99O3 catalyst with very low Ru loading (0.42 wt %) was stable over a 50 h DRM test and the carbon deposition was negligible. The CH4 and CO2 conversions at 750 °C reached 83 and 86%, respectively, approaching the theoretical thermodynamic equilibrium values.
ABSTRACT
It is important to develop highly active and stable catalysts for high temperature reactions, such as dry reforming of methane. Here we show a La(NiCo)OΔ (LNCO) submonolayer catalyst (SMLC) stabilized by the surface lattice of a perovskite LaCrO3 support and demonstrate a Ni-Co synergistic effect. The submonolayer/support type catalyst was prepared by in-situ hydrogen reduction of a LaNi0.05Co0.05Cr0.9O3 precursor synthesized by a sol-gel method. The LNCO-SMLC is highly active and very stable during a 100 h on stream test at 750 °C under the reaction conditions of dry reforming of methane. The catalyst also shows good anti-coking ability. We found that the synergistic effect between Ni and Co atoms in LNCO-SMLC remarkably improved the thermostability of the catalyst. This work provides a useful concept for designing atomically dispersed catalysts with high thermostability.
