No abstract

Developing low-cost, efficient, and robust nonprecious metal electrocatalysts for oxygen evolution reactions (OER) in acidic medium is the major challenge to realize the application of the proton exchange membrane water electrolyzer (PEM-WE). It is well-known that transition metal carbides (TMCs) have Pt-like electronic structures and catalytic behaviors. However, monometallic carbides in acidic medium show ignored OER activities. Herein, we reported that the catalytic activity of the TMCs can be enhanced by constructing bimetallic carbides (TiTaC2) fabricated through hydrothermal treatment followed by an annealing process, and further by doping fluorine (F) into the bimetallic carbides (TiTaF x C2). The as-prepared reduced graphene oxide (rGO) supported TiTaF x C2 nanoparticles (TiTaF x C2 NP/rGO) show state-of-the-art OER catalytic activity, which is even superior to Ir/C catalyst (an onset potential of only 1.42 V vs RHE and the overpotential of 490 mV to reach 100 mA cm–2), fast kinetics (Tafel slope of only 36 mV dec–1), and high durability (maintaining the current density at 1.60 V vs RHE for 40 h). Detailed structural characterizations together with density functional theory (DFT) calculations reveal that the electronic structures of the bimetallic carbides have been tuned, and their possible mechanism is also discussed.

Owing to the faster kinetics and outstanding catalytic performance, spinel oxides are regarded as a potential non‐precious metal electrocatalyst for oxygen evolution reaction (OER). Regulation of the geometrical structures of the spinel oxides is one of the most effective approaches for enhancing their OER performance. However, more wide and deep investigations remain because of the structural complexity of spinel oxides, for example, how to fill the unoccupied octahedral interstices to construct a large number of active sites for boosting the OER. Herein, iron foam (IF) supported NiFe2O4 nanocubes with high occupancy at octahedral sites (HOoct‐NFO NC/IF) are synthesized by hydrothermal method followed by anchoring and annealing. Detailed structural characterizations indicate that the foreign Fe cations can be filled into the octahedral interstices along the geometrical defects channel of transition metal cations coordinated with six oxygen anions (TMO6) by etching TMO6 units with an anchoring agent. As a result of the increasing of TMO5 sites with better activity and tuning of the electronic structures, the as‐fabricated HOoct‐NFO NC/IF electrocatalysts exhibit excellent performance for OER with overpotentials of 260 and 310 mV to reach 10 and 400 mA cm−2, respectively. Meanwhile, the catalysts show faster kinetics and superior stability.

The inferior activity of hydrogen oxidation reaction (HOR) in alkali severely hampers the deployment of Ni catalysts in the promising anion exchange membrane fuel cells (AEMFCs), due to the unbalanced binding energies of hydrogen (HBE) and hydroxyl (OHBE) species. Ni‐Mo alloy and nickel nitride have been proven to improve the Ni‐based activities of HOR but they still can be further enhanced. Because it sacrifices the HBE for enlarging OHBE. Herein, it is reported that the activity can be further improved by constructing heterostructure between Ni nanoparticles (NPs) and nitride of Ni‐Mo alloy (Ni0.2Mo0.8N) by an in situ synthetic strategy. The in situ prepared reduced graphene oxide (rGO) supported heterostructure (Ni/Ni0.2Mo0.8N/rGO) possesses the state‐of‐the‐art activity (overpotential of 100 mV to achieve 2.9 mA cm−2), faster kinetics (kinetics current density of 11.20 mA cm−2 and exchange current density of 2.74 mA cm−2), and ultrahigh durability (maintaining the current densities for over 40 h or 10000 cycles). Detailed characterizations together with density functional theory simulations reveal that the tuned d‐band electronic structures optimize and balance the HBE and OHBE, facilitating the HOR process on the as‐fabricated heterostructured catalyst.

Design and development of low‐cost and highly efficient non‐precious metal electrocatalysts for hydrogen evolution reaction (HER) in an acidic medium are key issues to realize the commercialization of proton exchange membrane water electrolyzers. Ni is regarded as an ideal alternative to substitute Pt for HER based on the similar electronic structure and low price as well. However, low intrinsic activity and poor stability in acid restrict its practical applications. Herein, a new approach is reported to encapsulate Ni nanoparticles (NPs) into interlayer edges of N‐doped Nb2CTx MXene (Ni NPs@N‐Nb2CTx) by an electrochemical process. The as‐prepared Ni NPs@N‐Nb2CTx possesses Pt‐like onset potentials and can reach 500 mA cm−2 at overpotentials of only 383 mV, which is much higher than that of N‐Nb2CTx supported Ni NPs synthesized by a wet‐chemical method (w‐ Ni NPs/N‐Nb2CTx). Furthermore, it shows high durability toward HER with a large current density of 300 mA cm−2 for 24 h because of the encapsulated structure against corrosion, oxidation as well as aggregation of Ni NPs in an acidic medium. Detailed structural characterization and density functional theory calculations reveal that the stronger interaction boosts the HER.