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Herein, a heterogeneous structure of Ni–Mo catalyst comprising Ni4Mo nanoalloys decorated on a MoOx matrix via electrodeposition is introduced. This catalyst exhibits remarkable hydrogen evolution reaction (HER) activity across a range of pH conditions. The heterogeneous Ni–Mo catalyst showed low overpotentials only of 24 and 86, 21 and 60, and 37 and 168 mV to produce a current density of 10 and 100 mA cm−2 (η10 and η100) in alkaline, acidic, and neutral media, respectively, which represents one of the most active catalysts for the HER. The enhanced activity is attributed to the hydrogen spillover effect, where hydrogen atoms migrate between the Ni4Mo alloys and the MoOx matrix, forming hydrogen molybdenum bronze as additional active sites. Additionally, the Ni4Mo facilitated the water dissociation process, which helps the Volmer step in the alkaline/neutral HER. Through electrochemical analysis, in situ Raman spectroscopy, and density functional theory calculations, the fast HER mechanism is elucidated. [ABSTRACT FROM AUTHOR]

The chemical coupling of molybdenum carbide (Mo2C) to cobalt (Co) promotes oxygen evolution reaction (OER) kinetics on the Co surface by making the surface more electrophilic. Here, to gain a deeper understanding of the effects of the surface electrophilic properties on the OER kinetics of Co and to obtain high OER activity, Fe and Ni are additionally incorporated into Co nanoparticles that are coupled with Mo2C nanoparticles (Co‐Mo2C). Considering the oxidation states of Fe (Fe3+), Co (Co2+/Co3+), and Ni (Ni2+) ions, Fe and Ni are expected to affect the electronic structure of Co in the opposite direction. Lewis acidic Fe3+ doping makes the Co surface oxide more electrophilic, promoting the formation of OER‐active CoOOH by strongly attracting hydroxide ions (OH−). Thus, the OER kinetics is facilitated on the Co surface of Fe‐doped Co‐Mo2C, resulting in a significantly lower overpotential for the OER. On the other hand, the Ni2+ doping makes the Co surface oxide less electrophilic, leading to an increase in the overpotential for the OER. Tailoring the electrophilic properties of the Co surface is presented as a key parameter in the design of a Co‐based OER catalyst for alkaline water electrolysis. [ABSTRACT FROM AUTHOR]

• TiO 2 -MoO x was prepared as a support for Ir catalyst toward OER. • Interaction between TiO 2 -MoO x and Ir promotes formation of OER-active Ir(III) species. • During the OER, the chemical Interaction between Mo and Ir keeps in Ir(III) species and suppresses dissolution of Ir. • Therefore, Ir/TiO 2 -MoO x exhibited improved OER activity and stability compared Ir black, Ir/C and Ir/TiO 2. • Ir/TiO 2 -MoO x improve performance and durability of the PEMWE single cell than Ir black. To accomplish the goals of cost reduction and durability improvement of polymer electrolyte water electrolysis (PEMWE), we report a titanium oxide and molybdenum oxide composite (TiO 2 -MoO x) as a support for the iridium (Ir) nanoparticle catalyst (Ir/TiO 2 -MoO x) toward oxygen evolution reaction (OER). Incorporation of Mo(V) and Mo(VI) into TiO 2 significantly enhances the electrical conductivity of TiO 2. During the synthesis of Ir nanoparticles on TiO 2 -MoO x , Mo(V) is oxidized to Mo(IV) with suppressing oxidation of Ir(III) to Ir(IV). Consequently, Ir/TiO 2 -MoO x forms higher fraction of the OER-active Ir(III) species on Ir surface enhancing OER activity of Ir catalyst. During OER, the chemical interaction between Mo and Ir keeps in Ir(III) and lessens the dissolution of Ir(III), improving the durability of Ir/TiO 2 -MoO x. Thus, Ir/TiO 2 -MoO x exhibits superior OER activity and durability. The single cell test results demonstrate that, as an anode catalyst, Ir/TiO 2 -MoO x can improve the performance and durability of the PEMWE cell than Ir black. [ABSTRACT FROM AUTHOR]