Iridium–Tungsten Alloy Nanodendrites as pH-Universal Water-Splitting Electrocatalysts

Abstract

The development of highly efficient and durable electrocatalysts for high-performance overall water-splitting devices is crucial for clean energy conversion. However, the existing electrocatalysts still suffer from low catalytic efficiency, and need a large overpotential to drive the overall water-splitting reactions. Herein, we report an iridium–tungsten alloy with nanodendritic structure (IrW ND) as a new class of high-performance and pH-universal bifunctional electrocatalysts for hydrogen and oxygen evolution catalysis. The IrW ND catalyst presents a hydrogen generation rate ∼2 times higher than that of the commercial Pt/C catalyst in both acid and alkaline media, which is among the most active hydrogen evolution reaction (HER) catalysts yet reported. The density functional theory (DFT) calculations reveal that the high HER intrinsic catalytic activity results from the suitable hydrogen and hydroxyl binding energies, which can accelerate the rate-determining step of the HER in acid and alkaline media. Moreover, the IrW NDs show superb oxygen evolution reaction (OER) activity and much improved stability over Ir. The theoretical calculation demonstrates that alloying Ir metal with W can stabilize the formed active iridium oxide during the OER process and lower the binding energy of reaction intermediates, thus improving the Ir corrosion resistance and OER kinetics. Furthermore, the overall water-splitting devices driven by IrW NDs can work in a wide pH range and achieve a current density of 10 mA cm–2 in acid electrolyte at a low potential of 1.48 V.

Recent Advances on Water‐Splitting Electrocatalysis Mediated by Noble‐Metal‐Based Nanostructured Materials

“…Taking W dopant as an example, IrW nanodendritic alloy with porous structure was fabricated by co‐reduction in an oleylamine system, showing excellent pH‐universal bifunctional catalysts exhibiting highly efficient activity toward overall water splitting (Figure 7). 49a The introduction of W not only tailors the electronic structure of Ir (active site) to tune H adsorption energy close to zero in acidic solution compared with pure Ir and Pt, but also W with stronger binding energy for OH* in favor of accelerating H 2 O dissociation in the alkaline media. In addition, the enhancement in OER activity of IrW/C can be ascribed to the downshift of d band center of Ir, weakening absorption of oxygen intermediates induced by alloying Ir with W. Besides the abovementioned 0D Ir‐based nanostructures, 1D nanostructures such as nanowires and nanotubes with additional advantages including unique property and stable structure have also attracted much more attention to drive full water splitting.…”

“…Copyright 2017, Wiley‐VCH. e–g) Reproduced with permission 49a. Copyright 2019, American Chemical Society.…”

Recent Progress in Bifunctional Electrocatalysts for Overall Water Splitting under Acidic Conditions

“…According to the volcano trends of HER and OER activities for transition metals, the Ir is positioned near the peak point, indicating that there is more room to be improved for the catalytic performance of Ir. Therefore, alloying of Ir with various transition metals has been a widely used strategy for climbing to the top of the activity trend . For instance, Lv and co‐workers reported a porous nanodendritic iridium‐tungsten alloy (IrW ND) as a bifunctional electrocatalyst for HER and OER .…”

Construction of Defect‐Rich RhCu Nanotubes with Highly Active Rh3Cu1 Alloy Phase for Overall Water Splitting in All pH Values

“…Unfortunately, both of the two half reactions are inefficient because the sluggish kinetics that come from electron/proton‐removal processes and the high activation barrier in decomposition reactions . In addition, electrocatalysts with bifunctional and highly active performance in wide pH values are more suitable for practical applications . However, many reported bifunctional electrocatalysts are usually applied in the basic medium for overall water splitting due to the harsh condition in the acid and the large onset overpotential in neutral medium .…”

“…However, the wide applications of pure noble metal electrocatalysts are limited by their high cost . Fortunately, alloying precious metal with non‐noble metal is an effective way to catalyze water splitting which can not only reduce the high price but also enhance electrochemical performance . For instance, Ir‐M (Fe, Co, Ni) electrocatalysts were synthesized for water‐splitting, which could reduce the use of metal Ir and facilitate the electrochemical performance due to the changing of the electronic properties of active center …”