Quantum-catalysis-enhanced extractable energy in a qubit quantum battery

In realistic open-system environments, decoherence and dissipation naturally drive quantum batteries toward passive states, thereby limiting their maximum extractable work (ergotropy). While quantum catalysis has been proposed to mitigate this degradation, the underlying thermodynamic mechanism remains not fully understood. Here, we investigate a driven qubit quantum battery coherently coupled to a harmonic-oscillator catalyst, subject to simultaneous dephasing and dissipation. By employing the differential first law of open quantum thermodynamics, we analyzed the dynamic energy balance to separate work and heat contributions during the charging process. We find that the catalyst induces a transient negative energy flux (energy backflow) into the qubit. This backflow actively counteracts decoherence-induced passivation and drives the battery into highly non-passive states, resulting in a pronounced enhancement of the ergotropy. Furthermore, we quantitatively establish the physical connection between this transient negative energy flux and the ergotropy gain. These results identify this transient negative energy flux as the operative thermodynamic mechanism, providing concrete physical insights for optimizing quantum energy-storage devices in noisy environments.