With the alarming depletion of fossil fuels, climate change and environmental degradation, environment sustainability and energy security have become a top priority. To this end, widespread adoption of renewable energy is deemed a promising strategy for meeting the growing global energy demands and addressing the related environmental issues. Most of the existing renewable energy conversion techniques are based on oxygen evolution reaction (OER), which is characterized by low efficiency due to sluggish kinetics. Addressing this limitation requires designing low-cost and high-performance catalysts for OER, which remains a big challenge.
Transition metal-based nanomaterials are an emerging lot for excellent OER catalysts. Generally, most transition metal-based electrocatalysts can undergo surface reconstruction during catalytic processes even though the surface evolution of multimetal-based catalysts and the structural-property relationship remains poorly understood. Considering the critical role of anions and cations in driving OER activity and properties, their regulation could lead to excellent transition metal-based electrocatalysts.
Synthesizing functional materials from waste has both environmental and economic benefits. Recycling and reusing urban solid wastes, especially recycling critical metals from electronic and electrical wastes like waste printed circuit boards (WPCBs), have drawn considerable attention, given their high economic value. Nevertheless, efficient recovery of the precious metals is yet to be fully realized, resulting in human health issues, severe ecosystem degradation and economic losses. This calls for an urgent design of a highly efficient recycling process for the effective management of WPCBs.
Herein, Dr. Zhijie Chen and Professor Bing-Jie Ni from the University of Technology Sydney together with Professor Hong Chen from the Southern University of Science and Technology developed a facile boriding strategy for direct conversion of multimetal cations in leachates of WPCBs into magnetic mixed metal borides (FeNiCuSnBs) for OER catalysts. This strategy involved integrating high-efficiency oxygen evolution catalysts with accelerated surface reconstruction from WPCBs. A total of four FeNiCuSnB samples, namely FNCSB-1 to FNCSB-4, were prepared via boriding chemical reaction and investigated. Their work is currently published in the journal, Applied Catalysis B: Environmental.
The authors reported the efficient recovery of Fe, Sn, Cu and Ni at a high metal cation recovery rate of 99.78%, 99.49%, 99.96% and 99.98%, respectively. The resulting as-mixed metal boride catalysts, especially those with higher Fe and Ni ratios, exhibited excellent catalytic performance for OER. Remarkably, the optimized FNCSB-4 sample exhibited good stability in alkaline solution and only needed a low overpotential of 199 mV to achieve a current density of 100 mA cm-2, representing the highest activity among the previously reported catalysts and studied waste-derived OER electrocatalysts.
An ex-situ characterization technique was adopted to elucidate the structure-activity relationship. Further mechanism analysis showed that the multimetal borides underwent an accelerated surface self-reconstruction induced by B/Sn etching and facilitated by the formation of the multimetal (oxy)hydroxides that served as active species for oxygen evolution. In addition, the amorphous feature, efficient charge/mass transfer and hierarchical structure also enhance the OER performance.
In summary, the authors are the first to develop a facile and efficient boriding strategy for the direct conversion of leachates of WPCBs into magnetic mixed metal borides for efficient OER. In addition to offering more insights into the correlation between the OER activity and surface self-reconstruction of the multimetal boride-based catalysts, the study findings also offered an efficient and sustainable strategy for recovering precise metals from electrical and electronic wastes. In a statement to Advances in Engineering, the first author, Dr. Zhijie Chen said that the proposed new strategy is a useful approach for regenerating efficient catalysts for high-efficiency critical metal recovery and reutilization.
Chen, Z., Zheng, R., Zou, W., Wei, W., Li, J., Wei, W., Ni, B., & Chen, H. (2021). Integrating high-efficiency oxygen evolution catalysts featuring accelerated surface reconstruction from waste printed circuit boards via a boriding recycling strategy. Applied Catalysis B: Environmental, 298, 120583.