Atmospheric Pressure Plasma Engineered Superhydrophilic Cuo Surfaces With Enhanced Catalytic Activities

Cupric oxide (CuO) thin film has found widespread application as a low-cost, earth-abundant material for electro and photo catalytic applications. High surface wettability is a key factor to achieve enhanced efficiency in these catalytic applications. Here, we report a fast and environment friendly route to fabricate super hydrophilic CuO thin films using a low power (5-10 W) atmospheric pressure plasma jet (APPJ). With APPJ treatment for 5 min, the CuO surface transforms from hydrophobic to super-hydrophilic with threefold increase in catalytic activity. The electrodes were extensively characterized using various bulk and surface-sensitive techniques. APPJ in-troduces anisotropy in the crystal structure and creates unique three-dimensional surface morphology with distinct surface chemical and electronic features. Interestingly, presence of oxygen in the plasma was found to be critical for the enhanced activities and the activity decreased when the functionalised with nitrogen plasma. Oxygen plasma functionalisation of CuO electrodes resulted in a 130 mV reduction in the onset potential for oxygen evolution reaction along with enhanced current density, 10 mA cm(-2) against 3 mA cm(-2) at 1 V vs Saturated Calomel Electrode in 0.1 M KOH without iR compensation. Importantly, without introducing any external dopants the work function could be decreased by 80 mV. Moreover, the treated films exhibited a higher rate of photo degradation (0.0283 min(-1) compared to 0.0139 min(-1)) of Methylene Blue and phenol indicating efficient charge separation. This work presents the potential of APPJ functionalisation of CuO surface to boost the activity of other thin film catalyst materials and solutions processed systems.