Sustainable corrosion management using natural deep eutectic solvents (NADES) in wind and solar energy systems: a review with focus on African context and opportunities

Corrosion remains one of the most economically and operationally significant threats to wind and solar energy infrastructure, yet conventional synthetic inhibitors predominantly chromate and phosphate-based compounds conflict with the environmental and sustainability objectives that underpin renewable energy transition. Natural deep eutectic solvents (NADES), eutectic mixtures of naturally occurring hydrogen bond acceptors and donors such as choline chloride paired with glycerol, organic acids, or sugars, have emerged as a compelling green alternative, combining biodegradability, low mammalian toxicity, 100% atom-economy synthesis at 50–100 °C, and wide compositional tunability. This review critically synthesizes the published literature on NADES as corrosion inhibitors, with specific contextualization for wind and solar energy infrastructure in sub-Saharan Africa - an application domain and geographic focus absent from all prior reviews on this topic. The physicochemical properties governing inhibitor performance are examined, including viscosity (50 to >5000 cP, tunable by controlled water addition), thermal stability, and hydrogen-bonding capacity, alongside the inhibition mechanisms revealed by electrochemical impedance spectroscopy, potentiodynamic polarization, and surface analytical techniques. Literature data show that optimized choline chloride-polyol and choline chloride-organic acid NADES achieve inhibition efficiencies exceeding 80% on mild steel and aluminium in acidic media through mixed-type adsorption-driven film formation, with Langmuir isotherm behaviour and standard Gibbs free energies of adsorption in the range −20 to −40 kJ mol- 1 . The review further establishes that agro-industrial residues widely available in Nigeria and South Africa, including cassava starch, palm oil-derived glycerol, and sugarcane-derived organic acids represent viable and strategically significant local feedstocks for NADES production, positioning this approach within Africa's circular economy framework. Critical gaps identified include the absence of field validation under cyclic wet-dry conditions, limited data on performance in chloride- and sulfur-rich coastal and industrial atmospheres, and the lack of techno-economic analyses comparing locally produced NADES against imported inhibitors. Addressing these gaps is essential to translating laboratory performance into reliable corrosion management solutions for Africa's expanding renewable energy sector.