Rational Construction of 3D Self‐Supported MOF‐Derived Cobalt Phosphide‐Based Hollow Nanowall Arrays for Efficient Overall Water Splitting At large Current Density

Abstract

Developing efficient nonprecious bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) in the same electrolyte with a low overpotential and large current density presents an appealing yet challenging goal for large‐scale water electrolysis. Herein, a unique 3D self‐branched hierarchical nanostructure composed of ultra‐small cobalt phosphide (CoP) nanoparticles embedded into N, P‐codoped carbon nanotubes knitted hollow nanowall arrays (CoPʘNPCNTs HNWAs) on carbon textiles (CTs) through a carbonization‐phosphatization process is presented. Benefiting from the uniform protrusion distributions of CoP nanoparticles, the optimum CoPʘNPCNTs HNWAs composites with high abundant porosity exhibit superior electrocatalytic activity and excellent stability for OER in alkaline conditions, as well as for HER in both acidic and alkaline electrolytes, even under large current densities. Furthermore, the assembled CoPʘNPCNTs/CTs||CoPʘNPCNTs/CTs electrolyzer demonstrates exceptional performance, requiring an ultralow cell voltage of 1.50 V to deliver the current density of 10 mA cm−2 for overall water splitting (OWS) with favorable stability, even achieving a large current density of 200 mA cm−2 at a low cell voltage of 1.78 V. Density functional theory (DFT) calculation further reveals that all the C atoms between N and P atoms in CoPʘNPCNTs/CTs act as the most efficient active sites, significantly enhancing the electrocatalytic properties. This strategy, utilizing 2D MOF arrays as a structural and compositional material to create multifunctional composites/hybrids, opens new avenues for the exploration of highly efficient and robust non‐noble‐metal catalysts for energy‐conversion reactions.

Carbon-Based Composites for Oxygen Evolution Reaction Electrocatalysts: Design, Fabrication, and Application

“…For comparison, by depositing CoNiCuMnAl@C on commercial carbon paper, the electrode achieved a current density of 100 mA cm −2 at 368 mV [126]. The protection role of the carbon layer at HCD was also confirmed by Kong et al [119]. They fabricated a 3D selfbranched hierarchical nanostructure composed of ultra-small CoP nanoparticles embedded into N,P-co-doped carbon nanotubes knitted hollow nanowall arrays (CoP@NPCNTs HN-WAs) on carbon textiles (CTs) via a carbonization-phosphatization process.…”

“…As previously mentioned, TMPs deliver superior OER activity. Great efforts have been made to develop not only TMP/carbon but also TMPs@carbon [118,119] electrocatalysts, creating a viable alternative to IrO 2 /RuO 2 -based electrocatalysts. Structural regulation is essential for realizing efficient and stable OER catalysis.…”

“…They fabricated a 3D selfbranched hierarchical nanostructure composed of ultra-small CoP nanoparticles embedded into N,P-co-doped carbon nanotubes knitted hollow nanowall arrays (CoP@NPCNTs HN-WAs) on carbon textiles (CTs) via a carbonization-phosphatization process. It exhibited superior electrocatalytic activity and stability in alkaline solutions [119]. It was capable of running for 200 h under the corresponding potential at 100 mA cm −2 .…”

“…It was capable of running for 200 h under the corresponding potential at 100 mA cm −2 . The assembled CoP@NPCNTs/CTs||CoP@NPCNTs/CTs electrolyzer achieved a high current density of 200 mA cm −2 at a low cell voltage of 1.78 V for OWS [119].…”

Advancing the Development of Hollow Micro/nanostructured Materials for Electrocatalytic Water Splitting: Current State, Challenges, and Perspectives

“…A 3D self-branched hierarchical nanostructure made of ultrasmall cobalt phosphide (CoP) NPs incorporated into Nand P-codoped CNTs knitted hollow nanowall arrays (CoP/ NPCNTs HNWAs) is synthesized by a carbonization− phosphatization process for electrocatalytic water splitting (Figure 13c). 118 Moreover, the combined electrocatalytic electrolyzer (CoP/NPCNTs/CTs || CoP/NPCNTs/CTs) shows remarkable performance, even reaching a high current density of 200 mA cm −2 at a low cell voltage of 1.78 V, needing an ultralow cell voltage of 1.50 V to achieve the current density of 10 mA cm −2 for overall water splitting with high stability. DFT calculation further shows that the most effective active sites in CoP/NPCNTs/CTs are the C-atoms between N and P atoms, greatly improving the electrocatalytic characteristics (Figure 13d).…”