The search for active and stable bifunctional electrocatalysts toward acidic overall water splitting is under increasing demand for the development of polymer electrolyte membrane (PEM) electrolyzers. However, developing bifunctional electrocatalysts with Pt-like activity and superior stability under acidic media still remains a big challenge. Herein, we report a successful synthesis of Ir wavy nanowires with an ultrathin diameter of 1.7 nm through a simple wet-chemical approach. Benefiting from the unique morphology with high aspect ratios and a large specific surface area, the as-synthesized ultrathin Ir wavy nanowires exhibit enhanced activity and durability for both the oxygen evolution reaction and the hydrogen evolution reaction in acidic electrolytes. Moreover, when used for overall acidic water splitting, a current density of 10 mA cm is achieved at only a cell voltage of 1.62 V in 0.1 M HClO electrolyte with long-term stability. In view of the excellent electrochemical water splitting performance and superior stability in acidic electrolytes, we believe that the obtained Ir wavy nanowires could be potential alternative catalysts toward PEM water electrolysis.

Developing highly efficient electrocatalysts and fundamentally understanding the mechanisms for alkaline hydrogen electrode reactions, including the hydrogen oxidation reaction (HOR) and the hydrogen evolution reaction (HER), are highly desirable. Here we report the synthesis of the IrMo alloy nanocatalyst and its outstanding HOR/HER performances under alkaline media. Specifically, the IrMo 0.59 exhibits the highest catalytic activities, which are 5 times higher than that of Ir and commercial Pt/C toward HOR and even a 10fold enhancement toward HER. Density functional theory (DFT) calculations reveal that H 2 O-occupied Mo sites on the surface of IrMo could effectively optimize the free energies of *H 2 O and *OH, thereby enable IrMo following the so-called bifunctional mechanism both in alkaline HER/HOR electrolysis.

Monodisperse IrNiFe alloy nanoparticles with an average diameter of 2.2 nm have been synthesized by a colloidal synthetic method. By taking advantage of the synergistic effect between Ir, Ni and Fe and the ultrasmall NPs with narrow size distribution, the as-synthesized IrNiFe catalyst exhibits superior HER/OER performances in acidic media.

Investigation of high-efficiency electrocatalysts for acidic overall water splitting is of great significance toward fulfillment of proton exchange membrane (PEM) electrolyzers but still remains challenging. Herein, we report the colloidally synthesis of IrCo alloy nanodendrites with petal-like architecture (NDs). Benefiting from unique hierarchical architecture and strong electronic interaction arising from synergistic alloying effect of IrCo at the atomic level, the resultant IrCo NDs display remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances with overpotentials of 17 and 281 mV to achieve 10 mA cm in 0.1 M HClO, respectively. Moreover, when further used as bifunctional electrocatalyst toward acidic overall splitting, a low cell voltage of 1.593 V is achieved at 10 mA cm.

A well-dispersed 3-in-1 IrW electrocatalyst with nanobranch architecture was synthesized and the catalyst exhibits excellent performance for HER and OER at all pH values. Furthermore, the IrW catalyst shows low cell voltages for overall water splitting in pH-universal electrolytes.