Electrochemical water splitting plays a crucial role in the development of clean and renewable energy production and conversion, which is a promising pathway to reduce social dependence on fossil fuels. Thus, highly active, cost‐efficient, and robust catalysts must be developed to reduce the reaction overpotential and increase electrocatalytic efficiency. In this review, recent research efforts toward developing advanced electrocatalysts based on noble metals with outstanding performance for water splitting catalysis, which is mainly dependent on their structure engineering, are summarized. First, a simple description of the water‐splitting mechanism and some promising structure engineering strategies are given, including heteroatom incorporation, strain engineering, interface/hybrid engineering, and single atomic construction. Then, the underlying relationship between noble metal electronic/geometric structure and performance for water splitting is discussed with the assistance of theoretical simulation. Finally, a personal perspective is provided in order to highlight the challenges and opportunities for developing novel electrocatalysts suitable for a wide range of commercial uses in water splitting for structural engineering applications.

The development of highly efficient bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial for improving the efficiency of overall water splitting, but still remains challenging issue. Herein, 3D self-supported Fe-doped Ni 2 P nanosheet arrays are synthesized on Ni foam by hydrothermal method followed by in situ phosphorization, which serve as bifunctional electrocatalysts for overall water splitting. The as-synthesized (Ni 0.33 Fe 0.67 ) 2 P with moderate Fe doping shows an outstanding OER performance, which only requires an overpotential of ≈230 mV to reach 50 mA cm −2 and is more efficient than the other Fe incorporated Ni 2 P electrodes. In addition, the (Ni 0.33 Fe 0.67 ) 2 P exhibits excellent activity toward HER with a small overpotential of ≈214 mV to reach 50 mA cm −2 . Furthermore, an alkaline electrolyzer is measured using (Ni 0.33 Fe 0.67 ) 2 P electrodes as cathode and anode, respectively, which requires cell voltage of 1.49 V to reach 10 mA cm −2 as well as shows excellent stability with good nanoarray construction. Such good performance is attributed to the high intrinsic activity and superaerophobic surface property.Herein, we fabricated self-supported Fe-doped Ni 2 P nanosheet arrays on the Ni foam by simple hydrothermal method and in situ phosphorization. The performance of Fe-doped Ni 2 P nanosheet arrays as bifunctional catalysts toward overall water splitting depends strongly on the Fe doping ratio in the Ni 2 P. The optimized Fe doping of Ni 2 P [(Ni 0.33 Fe 0.67 ) 2 P] showed excellent HER activity with an overpotential of ≈214 mV to reach 50 mA cm −2 and superior OER performance with a lower overpotential of ≈230 mV to reach 50 mA cm −2 , outperforming the commercial Ir/C. As expected, the electrolyzer using Ni 2 P nanosheet arrays with 31.7% Fe doping as both anode and cathode electrodes for catalyzing overall water splitting exhibited the best performance, obtaining a current density of 10 mA cm −2 at 1.49 V, better than the integration of commercial Pt/C and Ir/C electrodes.

A pine‐shaped Pt nanostructured electrode with under‐water superaerophobicity for ultrahigh and steady hydrogen evolution reaction (HER) performance is successfully fabricated by a facile and easily scalable electrodeposition technique. Due to the lower bubble adhesive force (11.5 ± 1.2 μN), the higher bubble contact angle (161.3° ± 3.4°) in aqueous solution, and the smaller size of bubbles release for pine‐shaped Pt nanostructured electrode, the incomparable under‐water superaerophobicity for final repellence of bubbles from submerged surface with ease, is successfully achieved, compared to that for nanosphere electrode and for Pt flat electrode. With the merits of superior under‐water superaerophobicity and excellent nanoarray morphology, pine‐shaped Pt nanostructured electrode with the ultrahigh electrocatalytic HER performance, excellent durability, no obvious current fluctuation, and dramatically fast current density increase at overpotential range (3.85 mA mV−1, 2.55 and 13.75 times higher than that for nanosphere electrode and for Pt flat electrode, respectively), is obtained, much superior to Pt nanosphere and flat electrodes. The successful introduction of under‐water superaerophobicity to in‐time repel as‐formed H2 bubbles may open up a new pathway for designing more efficient electrocatalysts with potentially practical utilization in the near future.

Exploring bifunctional catalysts for the hydrogen and oxygen evolution reactions (HER and OER) with high efficiency, low cost, and easy integration is extremely crucial for future renewable energy systems. Herein, ternary NiCoP nanosheet arrays (NSAs) were fabricated on 3D Ni foam by a facile hydrothermal method followed by phosphorization. These arrays serve as bifunctional alkaline catalysts, exhibiting excellent electrocatalytic performance and good working stability for both the HER and OER. The overpotentials of the NiCoP NSA electrode required to drive a current density of 50 mA/cm 2 for the HER and OER are as low as 133 and 308 mV, respectively, which is ascribed to excellent intrinsic electrocatalytic activity, fast electron transport, and a unique superaerophobic structure. When NiCoP was integrated as both anodic and cathodic material, the electrolyzer required a potential as low as ~1.77 V to drive a current density of 50 mA/cm 2 for overall water splitting, which is much smaller than a reported electrolyzer using the same kind of phosphide-based material and is even better than the combination of Pt/C and Ir/C, the best known noble metal-based electrodes. Combining satisfactory working stability and high activity, this NiCoP electrode paves the way for exploring overall water splitting catalysts.

No abstract

Layered double hydroxides (LDHs), especially Co-based LDHs, are regarded as a class of promising electrocatalysts toward overall water splitting, due to their good performance in oxygen evolution reaction (OER). However, inferior activity toward hydrogen evolution reaction (HER) hinders their scale-up applications. Here, a one-step hydrothermal strategy is proposed to fabricate 3D self-supported Rh-incorporated CoAl LDH (Rh/CoAl LDH) nanosheet arrays as bifunctional catalysts for overall water splitting. The thickness and lateral size of CoAl LDHs depend strongly on the introduced content of Rh atoms. Importantly, Rh incorporation distorts the local atomic arrangement owing to different atom sizes on the CoAl laminate. The strong interaction between Rh atoms and CoAl LDHs dramatically boosts the HER activity by facilitating HER kinetics and improves the OER performance simultaneously. The Rh/CoAl-300 LDH electrode with optimized composition only requires an overpotential of 71 mV to reach 10 mA/cm2 for HER and 390 mV to achieve 100 mA/cm2 for OER. The alkaline electrolyzer assembled by bifunctional Rh/CoAl-300 LDH electrodes only needs a cell voltage of 1.54 V at an overall water splitting of 10 mA/cm2.