Mo‐Modulated Eutectic Dealloying Unlocks Pt‐Competitive Hydrogen Evolution in Ni/Ni 0.91 Mo 0.09 via Hierarchical Sculpting and Ni Site Activation

Replacing platinum with highly active and durable Ni‐based catalysts is a critical challenge for scalable and cost‐effective hydrogen evolution reaction (HER). Here, a Mo‐modulated dealloying strategy enables a Mo‐modified Ni catalyst (containing merely 5 at% Mo) to achieve Pt‐competitive HER performance by synergistically engineering hierarchical architecture and electronic activation. Incorporating Mo into a Ni–Al precursor produces a unique “fishbone‐like” eutectic structure. Subsequent alkaline dealloying selectively dissolves the Mo‐rich phase and leaches Al from the Mo‐poor phase, sculpting a triple‐scale hierarchical porous Ni/Ni 0.91 Mo 0.09 composite (D‐Ni 4 Mo). This multi‐level porosity maximizes the electrochemically active surface area and promotes efficient mass transport. Concurrently, Mo‐doping coupled with lattice hole formation modulates the electronic structure of Ni sites, fully activating otherwise inert Ni atoms. The resulting D‐Ni 4 Mo catalyst requires only 75 mV overpotential at 500 mA cm −2 with an ultra‐low Tafel slope of 23.4 mV dec −1 , ranking the best among Pt‐based catalysts. Paired with a porous nickel‐iron anode (D‐Ni 4 Mo || D‐NiFe), the full electrolyzer requires only 1.61 V at 500 mA cm −2 and demonstrates remarkable stability for over 2000 h. This strategy pushes the performance boundaries of lightly alloyed nickel systems by precisely tailoring hierarchical structure and fully activating Ni‐sites.