Nitrogen-doped graphene nanoplatelets offer high catalytic performance in fuel cells and solar cells; possible replacement for Pt
Researchers in South Korea have developed a simple, low-cost and eco-friendly method of creating nitrogen-doped graphene nanoplatelets (NGnPs) with excellent catalytic performance in both dye-sensitized solar cells and fuel cells to replace conventional platinum (Pt)-based catalysts for energy conversion.
A paper on the work, carried out at Ulsan National Institute of Science and Technology (UNIST), is published in Scientific Reports. The UNIST team had previously reported that dry ball-milling can efficiently produce chemically modified graphene particles in large quantities. This new work dry ball mills graphite with nitrogen gas (N2), resulting in the direct fixation of N2 at the edges of graphene nanoplatelets (GnPs).
The mechanochemical cracking of graphitic C−C bonds generated active carbon species that react directly with N2 to form five- and six-membered aromatic rings at the broken edges, leading to solution-processable edge-nitrogenated graphene nanoplatelets (NGnPs).
...the search for economically viable alternatives to fossil fuels has attracted even increased attention among energy communities due to the continuously increasing energy price and global warming. Solar cells (SCs) and fuel cells (FCs) are considered to be promising alternatives. Although platinum (Pt)-based electrodes have been known to be the most efficient catalysts for dye-sensitized solar cells (DSSCs) and proton exchange membrane fuel cells (PEMFCs), they are too expensive and too susceptible to aggregation and poisoning impurities for practical applications.
Recently, much effort has been devoted to reduce or replace Pt-based electrodes. In particular, heteroatom-doped carbon-based materials, such as carbon black, carbon nanoparticles, carbon nanotubes and graphene nanoplatelets have been intensively studied as metal-free catalysts. However, the commonly used chemical vapor deposition (CVD) and/or Hummers’ methods for the production of carbon nanotubes and graphene are either too expensive for practical applications or involving environmentally hazardous reagents.
Therefore, the full potential of these carbon-based metal-free catalysts is hard to achieve without scalable production at low cost, though the basic catalytic mechanism has been established. The large quantity of the edge-nitrogenated graphene nanoplatelets (NGnPs) produced through such a simple, low-cost, and eco-friendly ball-milling process were further demonstrated to be effective metal-free catalysts for the replacement of precious Pt-based catalysts in DSSCs and PEMFCs for energy conversion. Therefore, the approach developed in this study can be regarded as a versatile technique toward multifunctional carbon nanomaterials of practical significance.—Jeon et al.
Investigating the photocatalytic activities of the NGnP electrodes as the counter electrode (CE) in actual devices in Co(bpy)3-mediated solar cells, the team found that the NGnP-based DSSC outperformed its Pt counterpart.
To investigate the electrocatalytic activity of NGnPs for oxygen reduction in fuel cells, they further measured the reduction capability of the NGnPs on glassy carbon (GC) in N2- and O2-saturated alkaline electrolytes. Pristine graphite and commercially available Pt/C with the same mass loadings on GC were also measured as references.
They found that the current density from NGnP is more than 2.8 times that of the pristine graphite and comparable to that of Pt/C. Furthermore, the NGnP electrode has high capacitances of 126.6 and 161.3 F g−1 with strong cycle stabilities in both N2− and O2−saturated electrolytes, which they attributed to the relatively high BET surface area and structural stability of NGnPs.
The solution-cast NGnP electrodes exhibited superior catalytic properties in DSSCs and FCs with respect to the precious Pt counterparts. Hence, direct nitrogen fixation developed in this study using ball-milling technique could be regarded as a general approach toward low-cost, mass production of NGnPs for multifunctional materials and devices applications.—Jeon et al.
This research was supported by World Class University (WCU), US-Korea NBIT, Mid-Career Researcher (MCR), Converging Research Center (CRC) and Basic Research Laboratory (BRL) programs through the National Research Foundation (NRF), of Korea funded by the Ministry of Science, ICT and Future Planning (Minister Choi Mun-Kee), US Air Force Office of Scientific Research through Asian Office of Aerospace R&D (AFOSR-AOARD), and AFOSR.
In-Yup Jeon, Hyun-Jung Choi, Myung Jong Ju, In Taek Choi, Kimin Lim, Jaejung Ko, Hwan Kyu Kim, Jae Cheon Kim, Jae-Joon Lee, Dongbin Shin, Sun-Min Jung, Jeong-Min Seo, Min-Jung Kim, Noejung Park, Liming Dai & Jong-Beom Baek (2013) Direct nitrogen fixation at the edges of graphene nanoplatelets as efficient electrocatalysts for energy conversion. Scientific Reports 3, Article number: 2260 doi: 10.1038/srep02260
In-Yup Jeon, Yeon-Ran Shin, Gyung-Joo Sohn, Hyun-Jung Choi, Seo-Yoon Bae, Javeed Mahmood, Sun-Min Jung, Jeong-Min Seo, Min-Jung Kim, Dong Wook Chang, Liming Dai, and Jong-Beom Baek (2012) Edge-carboxylated graphene nanosheets via ball milling PNAS doi: 10.1073/pnas.1116897109