Formation of a Cu@RhRu core-shell concave nanooctahedron via Ru-assisted extraction of Rh from the Cu matrix and its excellent electrocatalytic activity toward the oxygen evolution reaction

Bifunctional Ultrathin RhRu0.5 -Alloy Nanowire Electrocatalysts for Hydrazine-Assisted Water Splitting

Hydrazine-assisted water electrolysis offers a feasible path for low-voltage green hydrogen production. Herein, the design and synthesis of ultrathin RhRu_0.5 -alloy wavy nanowires as bifunctional electrocatalysts for both the anodic hydrazine oxidation reaction (HzOR) and the cathodic hydrogen evolution reaction (HER) is reported. It is shown that the RhRu_0.5 -alloy wavy nanowires can achieve complete electrooxidation of hydrazine with a low overpotential and high mass activity, as well as improved performance for the HER. The resulting RhRu_0.5 bifunctional electrocatalysts enable, high performance hydrazine-assisted water electrolysis delivering a current density of 100 mA cm^-2 at an ultralow cell voltage of 54 mV and a high current density of 853 mA cm^-2 at a cell voltage of 0.6 V. The RhRu_0.5  electrocatalysts further demonstrate a stable operation at a high current density of 100 mA cm^-2 for 80 hours of testing period with little irreversible degradation. The overall performance greatly exceeds that of the previously reported hydrazine-assisted water electrolyzers, offering a pathway for efficiently converting hazardous hydrazine into molecular hydrogen.

Recent progress in water-splitting electrocatalysis mediated by 2D noble metal materials

Two-dimensional (2D) nanostructures have enabled noble-metal-based nanomaterials to be promising electrocatalysts toward overall water splitting due to their inherent structural advantages, including a high specific surface active area, numerous low-coordinated atoms, and a high density of defects and edges. Moreover, it is also disclosed that the electronic effect and strain effect within 2D nanostructures also benefit the further promotion of the electrocatalytic performance. In this review, we have focused on the recent progress in the fabrication of advanced electrocatalysts based on 2D noble-metal-based nanomaterials toward water splitting electrocatalysis. First, fundamental descriptions about water-splitting mechanisms, some promising engineering strategies, and major challenges in electrochemical water splitting are given. Then, the structural merits of 2D nanostructures for water splitting electrocatalysis are also highlighted, including abundant surface active sites, lattice distortion, abundant surface defects, electronic effects, and strain effects. Additionally, some representative water-splitting electrocatalysts have been discussed in detail to highlight the superiorities of 2D noble-metal-based nanomaterials for electrochemical water splitting. Finally, the underlying challenges and future opportunities for the fabrication of more advanced electrocatalysts for water splitting are also highlighted. We hope that this review article provides guidance for the fabrication of more efficient electrocatalysts for boosting industrial hydrogen production via water splitting.

β-like FeOOH Nanoswords Activated by Ni Foam and Encapsulated by rGO toward High Current Densities, Durability, and Efficient Oxygen Evolution

As an alternative to the oxygen evolution reaction (OER) electrocatalyst developed by a complex bi- or multimetal ion with layered double hydroxide (LDH) structures, we design a simple, self-supported, and single-metal-ion OER electrocatalyst having lower overpotentials and high current densities in alkaline water electrolyzers. Here, β-like FeOOH nanosword structures encapsulated by reduced graphene oxide (rGO) were cost-effectively synthesized on formable Ni foam substrates as an efficient and highly durable OER catalyst. It is revealed that the rGO uniformly covered the β-like FeOOH nanoswords to form a porous network achieving a lower overpotential of only 210 mV at 10 mA cm^-2 with a stable operation for more than 40 h in alkali media. Moreover, a high current density of ∼300 mA cm^-2 was achieved at less than 1.8 V. In-depth physical and electrochemical analysis indicated that the intrinsic charge transfer through activated Ni-foam, β-like phase, and nanosword morphology was evidently beneficial for enhancing the OER activity of the bare FeOOH, and its encapsulation by rGO further improved the conductivity and long-life durability. Our integrated OER electrocatalyst developed by a simple method (repeated soaking and quenching process) will aid in scaling up β-like FeOOH nanoswords for preparing uniform and large-area electrodes for industrial purposes.

Iridium-Based Multimetallic Nanoframe@Nanoframe Structure: An Efficient and Robust Electrocatalyst toward Oxygen Evolution Reaction

Nanoframe electrocatalysts have attracted great interest due to their inherently high active surface area per a given mass. Although recent progress has enabled the preparation of single nanoframe structures with a variety of morphologies, more complex nanoframe structures such as a double-layered nanoframe have not yet been realized. Herein, we report a rational synthetic strategy for a structurally robust Ir-based multimetallic double-layered nanoframe (DNF) structure, nanoframe@nanoframe. By leveraging the differing kinetics of dual Ir precursors and dual transition metal (Ni and Cu) precursors, a core-shell-type alloy@alloy structure could be generated in a simple one-step synthesis, which was subsequently transformed into a multimetallic IrNiCu DNF with a rhombic dodecahedral morphology via selective etching. The use of single Ir precursor yielded single nanoframe structures, highlighting the importance of employing dual Ir precursors. In addition, the structure of Ir-based nanocrystals could be further controlled to DNF with octahedral morphology and CuNi@Ir core-shell structures via a simple tuning of experimental factors. The IrNiCu DNF exhibited high electrocatalytic activity for oxygen evolution reaction (OER) in acidic media, which is better than Ir/C catalyst. Furthermore, IrNiCu DNF demonstrated excellent durability for OER, which could be attributed to the frame structure that prevents the growth and agglomeration of particles as well as in situ formation of robust rutile IrO₂ phase during prolonged operation.