Ultrasonic Plasma Engineering Toward Facile Synthesis of Single-Atom M-N4/N-Doped Carbon (M = Fe, Co) as Superior Oxygen Electrocatalyst in Rechargeable Zinc–Air Batteries

Abstract

As bifunctional oxygen evolution/reduction electrocatalysts, transition-metal-based single-atom-doped nitrogen–carbon (NC) matrices are promising successors of the corresponding noble-metal-based catalysts, offering the advantages of ultrahigh atom utilization efficiency and surface active energy. However, the fabrication of such matrices (e.g., well-dispersed single-atom-doped M-N4/NCs) often requires numerous steps and tedious processes. Herein, ultrasonic plasma engineering allows direct carbonization in a precursor solution containing metal phthalocyanine and aniline. When combining with the dispersion effect of ultrasonic waves, we successfully fabricated uniform single-atom M-N4 (M = Fe, Co) carbon catalysts with a production rate as high as 10 mg min−1. The Co-N4/NC presented a bifunctional potential drop of ΔE = 0.79 V, outperforming the benchmark Pt/C-Ru/C catalyst (ΔE = 0.88 V) at the same catalyst loading. Theoretical calculations revealed that Co-N4 was the major active site with superior O2 adsorption–desorption mechanisms. In a practical Zn–air battery test, the air electrode coated with Co-N4/NC exhibited a specific capacity (762.8 mAh g−1) and power density (101.62 mW cm−2), exceeding those of Pt/C-Ru/C (700.8 mAh g−1 and 89.16 mW cm−2, respectively) at the same catalyst loading. Moreover, for Co-N4/NC, the potential difference increased from 1.16 to 1.47 V after 100 charge–discharge cycles. The proposed innovative and scalable strategy was concluded to be well suited for the fabrication of single-atom-doped carbons as promising bifunctional oxygen evolution/reduction electrocatalysts for metal–air batteries.

Engineering the Coordination Sphere of Isolated Active Sites to Explore the Intrinsic Activity in Single-Atom Catalysts

“…The high production of hydrogen through electrocatalytic water splitting is usually hindered by the kinetically sluggish OER. Therefore, highly efficient and robust SACs are urgently needed to enhance OER efficiency for minimizing the total overpotential for water splitting and other electronical applications [ 132 – 134 ]. Recently, Bao et al have anchored individual high-valence nickel atoms on graphene-like carbon via oxygen sites (Ni–O-G SACs) [ 135 ].…”

Recent Advances on MOF Derivatives for Non-Noble Metal Oxygen Electrocatalysts in Zinc-Air Batteries

“…Platinum/iridium-based catalysts are often benchmark electrocatalysts used to improve oxygen electrolysis in ZABs [ 87 , 88 ], reducing the catalyst loading and increasing intrinsic catalytic activity of these noble metal-based oxygen electrocatalysts are critical to realizing their application on large-scale. In this regard, single-atomic catalysts (SACs) are promising due to favorable active sites uniformity, high product selectivity, multiple support types, high atomic efficiency and low precious metal usage [ 89 – 91 ]. However, it is difficult and challenging to synthesize SACs because with the dispersion of catalysts at the atomic level, the surface free energy increase sharply leading to serious aggregation [ 92 ].…”

Folic Acid Self-Assembly Enabling Manganese Single-Atom Electrocatalyst for Selective Nitrogen Reduction to Ammonia

“…However, the thermodynamically unstable nature of single metal atoms poses challenges for preparing stable SACs. To successfully engineer SACs, suitable precursors (including metal and supporting materials), effective synthetic strategies and intriguing metalsupport interactions are three important considerations, which are also intimately correlated with the exotic geometric and electronic structures of SACs [22,24,25]. As a representative, Mn single-atom catalysts (Mn SACs) with Mn δ+ -N x sites have been developed and proved to be highly active for CO 2 reduction and oxygen reduction; however, they have seldom been explored for NRR [26][27][28][29][30].…”