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In this work, a novel system composed of non-precious nickel-based metal oxide/reduced graphene oxide nanocomposite (Ni–PbO2–GN) is used for electrooxidation of ethylene glycol (EG) in 1.0 M NaOH solution and compares its activity with that of Ni, Ni–GN, and Ni–PbO2. The facile electrodeposition technique is used to prepare the catalysts on glassy carbon (GC) substrates. The outcomes of electrochemical measurements show a high performance towards EG oxidation is obtained for Ni-nanocomposite electrodes compared to that of Ni mainly due to their higher surface areas. The excellent electrocatalytic properties of the Ni-nanocomposite could be ascribed to the synergistic contributions of PbO2 and graphene (GN) nano-sheets that help the reduction of Ni grains. A smaller charge transfer resistance value of 34.5 Ω cm2 for EG oxidation reaction at + 360 mV is recorded for GC/Ni–PbO2–GN compared to the other prepared electrodes. Moreover, it exhibits higher kinetic parameters of EG such as diffusion coefficient (D = 3.9 × 10–10 cm2 s−1) and charge transfer rate constant (ks = 32.5 mol−1 cm3 s−1). The overall performance and stability of the prepared catalysts towards EG electrooxidation have been estimated to be in the order of GC/Ni–PbO2–GN > GC/Ni–GN > GC/Ni–PbO2 > GC/Ni. Graphical abstract

This paper presents a robust sliding-mode control technique to be applied to quaternion-based attitude control for rest-to-rest maneuvers with external disturbances. A sliding mode controller has been designed to force the state variables of the closed loop system to converge to the desired values. A control strategy is designed based on a novel mathematical rule that computes the discontinuous feedback gains. The proposed approach is defined in such a way that the selected controller parameters can drive the state to hit the sliding surface fast and then keep the state sliding along the surface with less chattering and tracking error. Moreover, the control parameters are adjusted to avoid the body angular velocity reached the upper limit during the maneuver. A simulation model of the controlled spacecraft system was developed in MATLAB-SIMULINK software. The phase portraits and the state plots prove the control technique power. The "chattering" problem of the sliding mode control has been adopted using variable thickness boundary layer technique. The second method of Lyapunov is used to guarantee the system stability under the proposed control laws action. Simulations have been carried out to demonstrate and verify the developed controller performance.

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