Electrocatalytic oxidation for hydroxyl radicals generation: Exploring the role of an electrode-induced interphase on electronically controlled solid propellants

The controllability of thrust is paramount for electronically controlled solid propellants (ECSPs), which rely on the rapid redox reaction of hydroxylamine nitrate (HAN) as their primary oxidant. This study proposes a mechanism for HAN-electrolysis and electrode-induced solid propellant interphases (SPIs). The electrocatalytic oxidation of hydroxylamine in HAN plays a crucial role in the formation of interphases with copper, stainless steel, and titanium electrodes. The resulting hydroxyl radical oxidizes these electrodes to produce SPIs and also oxidizes polyvinyl alcohol to accelerate the thermal decomposition. The current density on the combustion process is significantly influenced by SPIs, determining whether the combustion state is electrolytically-led rapid combustion or pyrolytically-led slow combustion. SPIs with different electrodes are identified as Cu 2 (NO 3 )(OH) 3 , Fe(OH) 3 , and a mixture of the thermal decomposition of the propellants, respectively. Cu 2 (NO 3 )(OH) 3 has the smallest energy gap and impedance, resulting in the highest current density and optimal performance. The gas production of the Cu electrode is about 3.8 times that of the stainless steel electrode and about 6.7 times that of the Ti electrode at the same conditions. The in-situ SPIs are substituted with Cu 2 (NO 3 )(OH) 3 as the interface layer, leading to increased gas production for the copper electrode (by 3 times), stainless steel electrode (by 5.7 times), and titanium electrode (by 4.2 times). This research introduces the effects of SPIs and the electrocatalytic oxidation of hydroxylamine, offering a direction for improving the thrust and controllability of ECSPs.