As the central component of any battery system, electrode materials directly determine energy efficiency, power density, and overall lifespan. Improving their performance has therefore remained the key focus of flow-battery R&D. This review systematically summarizes the strategies and recent progress for enhancing two core performance metrics—electrical conductivity and stability—and looks ahead to future directions.

High conductivity is the prerequisite for low internal resistance and high energy efficiency. Improvements are pursued along three main lines: substrate selection, micro-structure tuning, and synergistic composites. Among carbon substrates, graphene, carbon nanotubes (CNTs), and highly crystalline graphite are prioritized for their outstanding conductivity; among metals, Cu, Ni, and Ag are excellent conductors but require cost-stability trade-offs. Micro-structural optimization includes high-temperature graphitization to reduce defects (sp³ carbons, edge sites, oxygen functionalities) that hinder carrier mobility, and the construction of 3-D interconnected conductive scaffolds from 1-D CNTs or 2-D graphene to shorten ion/electron pathways (e.g., CNT-decorated carbon felts that markedly lower contact resistance). Composite synergy is another powerful route: carbon-metal hybrids (e.g., Ni-nanoparticle-decorated graphene) exploit the high conductivity of metal nanoparticles or nanowires; carbon-conducting-polymer hybrids combine PANI, PPy, or similar polymers with carbons to preserve conductivity while adding active sites and functionality.

Stability governs long-term reliability and is addressed via surface engineering and intrinsic material optimization. The most direct approach is protective coatings: corrosion-resistant layers (noble metals/oxides such as Pt, Ru, Ir; transition-metal oxides like TiO₂, MnO₂) isolate the carbon from aggressive electrolytes, raising oxidation/reduction stability at extreme potentials; carbon coatings (CVD-derived pyrolytic carbon or graphene) seal surface defects and form dense protective films. Catalytic functionalization (Bi, Pt, or N/S-containing groups) lowers activation energies for key reactions, accelerates kinetics, and simultaneously enhances stability. Intrinsic strategies include using naturally passivating metals (Ni, Ti in alkaline all-iron flow batteries) that form self-protective films; defect engineering and heteroatom doping (N, B, P) in carbons to tailor electronic structures, boosting both catalytic activity and local chemical robustness; and interfacial reinforcement in composites to suppress delamination or component segregation under long-term stress or corrosion.

Composites are the frontier for multi-objective optimization of conductivity, stability, and catalytic activity. Carbon-metal hybrids (e.g., Ni-nanowire/graphene, Cu-mesh/carbon felt) combine the light weight, high surface area, and flexibility of carbon with the high conductivity and mechanical strength of metals, but interfacial compatibility and metal dissolution during cycling remain challenges. Carbon-conducting-polymer hybrids (e.g., PEDOT:PSS-coated carbon paper, PANI/graphene aerogels) leverage the flexibility, functional groups, and catalytic activity of polymers to complement the rigid, highly conductive carbon scaffold, though polymer aging under prolonged cycling or harsh conditions must be mitigated. Designing hierarchical porosity from nano- to micro-scale (micro-pores for surface area and active sites; meso- and macro-pores for electrolyte transport) and precisely tailoring surface chemistry (type and density of functional groups) are crucial for maximizing overall performance.

Despite significant advances, key challenges persist. Cost control: high-performance materials (graphene, CNTs, noble-metal coatings) and complex processes (CVD) hinder scale-up; scalable, low-cost synthesis/modification (wet-chemistry, electrodeposition) is urgently needed. Long-term stability validation: accelerated lab aging cannot fully mimic real-world decay over years or decades; reliable lifetime-prediction models and long-cycle standards are required. Performance balancing: conductivity, stability, catalytic activity, and low cost are mutually constraining; multi-scale design (atomic doping, nano-architecturing, macro-electrode engineering) and defect engineering (controlled beneficial defects) are essential for precise optimization.

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