John Edward Graves

In recent years, the demand for lithium-ion batteries (LIBs) has been increasing rapidly. Conventional recycling strategies (based on pyro- and hydrometallurgy) are damaging for the environment and more sustainable methods need to be developed. Bioleaching is a promising environmentally friendly approach that uses microorganisms to solubilize metals. However, a bioleaching-based technology has not yet been applied to recover valuable metals from waste LIBs on an industrial scale. A series of experiments was performed to improve metal recovery rates from an active cathode material (LiCoO₂; LCO). (i) Direct bioleaching of ≤0.5 % LCO with two prokaryotic acidophilic consortia achieved >80 % Co and 90 % Li extraction. Significantly lower metal recovery rates were obtained at 30 °C than at 45 °C. (ii) In contrast, during direct bioleaching of 3 % LCO with consortia adapted to elevated LCO levels, the 30 °C consortium performed significantly better than the 45 °C consortium, solubilizing 73 and 93 % of the Co and Li, respectively, during one-step bioleaching, and 83 and 99 % of the Co and Li, respectively, during a two-step process. (iii) The adapted 30°C consortium was used for indirect leaching in a low-waste closed-loop system (with 10 % LCO). The process involved generation of sulfuric acid in an acid-generating bioreactor (AGB), 2–3 week leaching of LCO with the biogenic acid (pH 0.9), selective precipitation of Co as hydroxide, and recirculation of the metal-free liquor back into the AGB. In total, 58.2 % Co and 100 % Li were solubilized in seven phases, and >99.9 % of the dissolved Co was recovered after each phase as a high-purity Co hydroxide. Additionally, Co nanoparticles were generated from the obtained Co-rich leachates, using Desulfovibrio alaskensis, and Co electrowinning was optimized as an alternative recovery technique, yielding high recovery rates (91.1 and 73.6% on carbon felt and roughened steel, respectively) from bioleachates that contained significantly lower Co concentrations than industrial hydrometallurgical liquors. The closed-loop system was highly dominated by the mixotrophic archaeon Ferroplasma and sulfur-oxidizing bacteria Acidithiobacillus caldus and Acidithiobacillus thiooxidans. The developed system achieved high metal recovery rates and provided high-purity solid products suitable for a battery supply chain, while minimizing waste production and the inhibitory effects of elevated concentrations of dissolved metals on the leaching prokaryotes. The system is suitable for scale-up applications and has the potential to be adapted to different battery chemistries.

Nitrided steel is being used to increase the lifetime and wettability of selective soldering nozzles. In this environment, the liquid solder wets to the surface of the nozzle to enable control of the solder flow during the soldering process. Pre-treatment is a key step in the processing of parts for electroplating. Pre-treatment usually involves degreasing and acidic pickling steps in order to remove adsorbed oil-based compounds and oxides respectively. These steps ensure a well-structured and adherent electroplated coating to the part. Surface treatments such as nitriding alter the surface composition of steels and thereby change the conductivity/surface activity. Typically, a nitrided surface contains a dual-phase surface layer followed by a diffusion zone consisting of the formed nitrides and finally a transition zone to the bulk material. Generally, this surface treatment is performed to harden materials without the risk of dimensional changes. For a selective soldering application, it reduces the dissolution of material into the solder during operation while also improving the wetting of the nozzle. The electroplated coatings for the selective soldering nozzles consist of 10 microns of nickel and 10 microns of tin. This structure allows for near-instant wetting and use of the nozzle. Furthermore, the electroplated layers provide corrosion protection for the nozzle ensuring no oxide or scale layers will form that may require flux for cleaning. A range of chemical and electrochemical pre-treatment steps were explored to prepare and optimally activate the nitride-hardened steel surfaces for electroplating. The processes included: hot degreasing and electrolytic degreasing with alkaline detergents; electrolytic descaling in a solution containing sodium hydroxide; chemical pre-descaling process with potassium permanganate; varying the compositions of pickling in inorganic acids; different formulations for nickel strike electrolytes for plating onto ferrous alloys. Mass loss measurements provided an estimation of the thickness of the material removed due to acid pickling. Scanning electron microscopy was employed to assess changes in the surface due to the pre-treatment. Open circuit potential measurements were applied to measure the surface activity before any pre-treatment and also the change in surface conductivity/activity post-treatment. Nanoindentation measurements were used to assess the change in surface hardness as a result of the nitriding treatment and also to check for the presence of the remaining hardened nitrided layer after pre-treatment. Glow discharge optical emission spectroscopy was utilised to study the elemental depth profile of the nitrided parts. Crystalline structure was studied through x-ray diffraction. After pre-treatment, a Woods nickel strike was applied to prepare the surface for further electroplating with bright tin. SEM analysis of the cross-sections of the coated specimens was used to analyse the coating microstructure. Thickness of the electrodeposited coatings were confirmed with x-ray fluorescence. Thermal shock tests were performed to confirm that the adhesion of the coating was sufficient. Approximately half of the nitrided layer was removed by pre-treatment in order to activate the surface for electroplating. More severe pre-treatment was required compared to electroplating non-hardened parts to activate the surface. Surface conductivity/surface activity was altered as measured by OCP resulting from the pre-treatment. This work has analysed the surface modification of nitride-hardened steels during the pre-treatment steps required to initiate electroplating and has shown that it is possible to prepare nitride-treated steels for electroplating. The results can be used to develop more optimal pre-treatment processes for electroplating nitrided steels.

Water electrolysis is believed to be one of the most promising technologies to produce green hydrogen. However, the current challenge in commercialising this technology is the high relative cost. According to a recent report on cost breakdown of Polymer Electrolyte Membrane (PEM) electrolyser [1], the cell stack contributes to 35% - 45% of the total cost. Catalyst materials on the electrodes are believed to be the primary areas for innovation and cost reduction in PEM electrolysers. Several approaches have been applied to reduce the stack cost, with a focus on reducing material usage while enhancing the performance of PEM electrolysers. This project aims to reduce catalyst loading on the anode of PEM water electrolyser while maintaining high performance, through developing an inkjet printing technique to create a thin, porous and active catalyst layer. Conventional catalyst fabrication techniques such as spray coating produce large amount of material waste and non-homogenous distribution on the surface [2]. Inkjet printing will provide controlled catalyst loading, ensuring well catalyst distribution, creating porous structure, and having the ability to create patterned electrodes [3]. Due to its high activity, Iridium Oxide (IrO₂) is selected as the catalyst. The ink was formulated to be compatible with the printing requirement, with 7.5 wt% of IrO₂ powder, 7.9 wt% of Nafion, and 84.5 wt% of solvents mixture of Isopropanol and Propylene Glycol. Full coverage of the catalyst on the Titanium substrate was proven by Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Analysis (EDX). The effect on varying the number of printed layers was analysed in terms of catalyst loading and activity to show a linear increase in activity with the number of layers. Moreover, electrochemical performance was inspected using cyclic voltammetry in a 3-electrodes cell. The printed electrodes showed comparable stability to conventional electrodes. Electrochemical surface area (ECSA) was higher for the 10-layered electrodes as compared to the 2-layered electrodes indicating higher catalyst utilisation. Printed electrodes showed activity of 300 mA/mg IrO₂ with ECSA of 225 cm² at reduced catalyst loading of 0.8 mg IrO₂/cm². These results outperform conventionally fabricated electrodes by spray and decal transfer coatings [4]. References [1] A. T. Mayyas, M. F. Ruth, B. S. Pivovar, G. Bender, and K. B. Wipke, “Manufacturing Cost Analysis for Proton Exchange Membrane Water Electrolyzers,” NREL/TP-6A20-72740, 1557965, Aug. 2019. doi: 10.2172/1557965. [2] W. Qing, F. Liu, H. Yao, S. Sun, C. Chen, and W. Zhang, “Functional catalytic membrane development: A review of catalyst coating techniques,” Adv. Colloid Interface Sci., vol. 282, p. 102207, Aug. 2020, doi: 10.1016/j.cis.2020.102207. [3] J.-J. Chen, G.-Q. Lin, Y. Wang, E. Sowade, R. R. Baumann, and Z.-S. Feng, “Fabrication of conductive copper patterns using reactive inkjet printing followed by two-step electroless plating,” Appl. Surf. Sci., vol. 396, pp. 202–207, Feb. 2017, doi: 10.1016/j.apsusc.2016.09.152. [4] Z. Xie et al., “Optimization of catalyst-coated membranes for enhancing performance in proton exchange membrane electrolyzer cells,” Int. J. Hydrog. Energy, vol. 46, no. 1, pp. 1155–1162, Jan. 2021, doi: 10.1016/j.ijhydene.2020.09.239.

In the present study, a model of closed-loop recycling of copper from PCBs is demonstrated, which involves the sequential application of bioleaching and electrowinning to selectively extract copper. This approach is proposed as part of the solution to resolve the challenging ever-increasing accumulation of electronic waste, e-waste, in the environment. This work is targeting copper, the most abundant metal in e-waste that represents up to 20% by weight of printed circuit boards (PCBs). In the first stage, bioleaching was tested for different pulp densities (0.25–1.00% w/v) and successfully used to extract multiple metals from PCBs using the acidophilic bacterium, Acidithiobacillus ferrooxidans. In the second stage, the method focused on the recovery of copper from the bioleachate by electrowinning. Metallic copper foils were formed, and the results demonstrated that 75.8% of copper available in PCBs had been recovered as a high quality copper foil, with 99 + % purity, as determined by energy dispersive X-ray analysis and Inductively-Coupled Plasma Optical Emission Spectrometry. This model of copper extraction, combining bioleaching and electrowinning, demonstrates a closed-loop method of recycling that illustrates the application of bioleaching in the circular economy. The copper foils have the potential to be reused, to form new, high value copper clad laminate for the production of complex printed circuit boards for the electronics manufacturing industry. Graphic Abstract

A novel approach to selective electroless deposition of metal on non-conductive substrates was developed. Using an electroless copper process requires the non-conductive material to be catalysed prior to electroless deposition and this is typically carried out using a Pd-Sn colloidal catalyst. In the current work, a novel magnetic Fe₃O₄-Ag nanoparticle (NP) catalyst was used. The composite particles were obtained by a wet chemical method. The composition, particle size and crystal structure of the particles were confirmed by transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The magnetic properties were characterised by vibrating sample magnetometry whilst the catalytic activity towards formaldehyde oxidation (the key reaction in electroless copper deposition) was confirmed by cyclic voltammetry. Because this new catalyst is magnetic, a magnetic field gradient can be used to manipulate the catalyst NPs. A permanent magnet was attached to the constructed steel template so that a magnetic field gradient on the FR-4 laminate substrate surface was achieved. When the magnetic field was applied, the Fe₃O₄-Ag catalyst NPs were attracted only to the areas of maximum magnetic field gradient on the surface, leading to selective catalysation of the substrate. Subsequent electroless copper plating only occurred at the areas where the composite magnetic NPs were deposited, meaning that selective metallisation by applying a magnetic field was achieved. The width of the selectively metallised lines was 350±20 μm.