• • AWE systems achieve low equipment construction cost but suffer from low electrolytic efficiency, typically <70% at current densities below 0.5 A cm⁻², necessitating efficiency enhancements to compete with PEM.
• • PEM electrolyzers deliver higher hydrogen production rates but rely on precious metal catalysts (e.g., Pt, Ir) and high-performance membranes, resulting in production costs exceeding $2000 per kW, which impedes cost parity with gray hydrogen.
• • AEM combines advantages of AWE and PEM, showing potential for both low cost and high efficiency, yet durability remains insufficient, with degradation rates >100 μV h⁻¹ under industrial conditions.
• • Innovative designs such as semi-vapor electrolyzers and flow-engineered 3D electrodes enable operation at current densities up to 2 A cm⁻² with reduced ohmic losses, potentially lowering hydrogen production cost to <$2 per kg.