Reusing Waste Coffee Grounds as Electrode Materials: Recent Advances and Future Opportunities

Abstract

202200093400 billion cups per year and an annual growth of 1.3% since 2012/2013. [50,51] An average cup of coffee has roughly 11 g of ground coffee, which equates to over 9 million tons of ground coffee being brewed worldwide per annum. The global consumption of coffee over the last decade has steadily increased to over 10 million tons by 2021, and this increase is clearly illustrated by Figure 1. For every 1 kg of coffee grounds used within the beverage industry, roughly 0.9 kg is discarded as waste. This has led to millions of tons of waste coffee grounds (WCG) per year. [52] When these WCG is disposed of as landfill waste, they decompose and emit methane which is a potent greenhouse gas (25 times more potent than carbon dioxide over 100 years period) with severe adverse effects to the environment. [50] In addition, the leachates and soluble from WCG in landfill and via sewage was also found to cause DNA damage and thus induce genotoxicity in aquatic organisms. [53] In recent years, the concept of circular economy began to gain traction and most leading countries have been increasing the efforts to shift their economy toward this paradigm. Circular economy aims for economic activities to build and rebuild overall system health by reducing or eliminating the overall amount of waste in society via recycling and reusing products. [55,56] As the coffee is mainly disposed as waste after its initial brew and these WCG can pose a significant environmental risk in landfill (i.e., green gas emission and leachate-induced mutagenicity), it is imperative to find applications of WCG and thus promoting the transition to the circular economy in food industry. On the other hand, as one of the most abundant types of food waste, WCG contains a high volume of valuable sources of carbon and yet remains largely unexploited by industry at the moment. According to a study that investigated chemical, functional, and structural properties of WCG, [57] its most abundant components were found to be macro molecules of cellulose and hemicellulose structures which are polymeric structures of hexose saccharides. These two structures can account for 51.50% w/w of the total mass on a dry weight basis. Second highest component was found to be lignin, a highly aromatic structure comprised of crosslinked phenolic structures, which can be up to 40% w/w based on a sulfuric acid hydrolysis extraction. [58] The rest of WCG composition includes fatty and amino acids, polyphenols, caffeine, tannins, and minerals, [45] etc.Coffee industry produces more than eight million tons of waste coffee grounds (WCG) annually. These WCG contain caffeine, tannins, and polyphenols and can be of great environmental concern if not properly disposed of. On the other hand, components of WCG are mainly macromolecular cellulose and lignocellulose, which can be utilized as cheap carbon precursors. Accordingly, various forms of carbon materials have been reportedly synthesized from WCG, including activated carbon, mesoporous carbon, carbon nanosheets, carbon nanotubes, grap...

Porous Carbon Nanosheets Derived from Spent Coffee Grounds for Highly Stable Electric Double-Layer Capacitors Enabled by Structurally Complementary Carbons

“…Yu et al proposed a model to generate desired thickness and pore structures of 2D PCNs with fast ion transport for high-energy-density supercapacitors . Several significant accomplishments have recently been completed using SCGs as precursors to yield 2D PCNs as the crucial electrode material for supercapacitors. − Most recently, a review article thoroughly described the recent advances and future opportunity for reusing SCGs as electrode materials for energy storage devices . These studies demonstrate a clear vision for converting SCGs into high-value materials with the potential for mass production.…”

“…These studies demonstrate a clear vision for converting SCGs into high-value materials with the potential for mass production. However, as we all know, the critical shortcomings of supercapacitors, such as inferior energy density, high levelized cost, long-life instability, and rapid self-discharge rates, remain to be solved before they are practicable in commercial products. , Therefore, more research is required to assemble an EDLC electrode with designable materials and to deliver highly stable behaviors during charge–discharge cycles, a low self-discharge rate, and a high energy density …”

“…However, as we all know, the critical shortcomings of supercapacitors, such as inferior energy density, high levelized cost, long-life instability, and rapid selfdischarge rates, remain to be solved before they are practicable in commercial products. 31,32 Therefore, more research is required to assemble an EDLC electrode with designable materials and to deliver highly stable behaviors during charge− discharge cycles, a low self-discharge rate, and a high energy density. 32 In this study, we propose a new approach to generate 2D PCNs (thickness between 6−10 nm) derived from SCGs, denoted as AC2500 with a specific surface area of 2498 m 2 g −1 and a total volume reaches 1.2 cm 3 g −1 , mainly in mesopore structures) by combining two structurally complementary conductive carbon blacks (CBs) [Super P (a high-graphitic CB) and BP2000 (a high disorder and porous CB)].…”

“…24−30 Most recently, a review article thoroughly described the recent advances and future opportunity for reusing SCGs as electrode materials for energy storage devices. 31 These studies demonstrate a clear vision for converting SCGs into high-value materials with the potential for mass production. However, as we all know, the critical shortcomings of supercapacitors, such as inferior energy density, high levelized cost, long-life instability, and rapid selfdischarge rates, remain to be solved before they are practicable in commercial products.…”

Ginsentide-like Coffeetides Isolated from Coffee Waste Are Cell-Penetrating and Metal-Binding Microproteins

“…Among >100 species of Coffea, C. canephora , also known as C. robusta , is the second most commonly planted species because it can reach great crop yields [ 19 ]. However, coffee processing generates about 50% of waste, mainly coffee pulp and husk [ 19 , 20 ]. Based on the ethnomedicinal uses of coffee plants, it is likely that bioactive compounds are present in coffee waste.…”