Inorganic Chemistry Frontiers Blog

The effective use of earth abundant electrocatalyst copper in splitting of water as nanostructures with different combinations is central in replacing the noble metals for the industrialization of hydrogen generation. Being the carbonaceous fuels as front line suppliers of energy, they adversely lead to affect the environment with the greenhouse gases emission. Considering the electrocatalytic way of splitting water, it is one of the finest ways of producing pure hydrogen with fast rate and assisted with no other undesired by-products and hence researchers across the world focus maximum attention to make it commercially applicable.

To replace the noble metals, transition metals based catalysts are promising and the importance of Cu based nanostructures as effective electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) needs greater attention. Moreover, various synthetic approaches with Cu nanostructures like mono, bi and tri metallic catalysts as oxides hydroxides, sulfides, selenides, tellurides and phosphides were studied for OER and HER in different pH conditions will give a vast analysis on Cu based catalysts towards real scale water splitting electrocatalytically.

Hence, to precise, a brief understanding on Cu-based nanostructures in electrocatalytic water splitting is highly needed to be applied with other advancements in catalysts development for the viable hydrogen generation with electrocatalytic water splitting.

Recently, Karthick. K and Subrata Kundu and co-authors have highlighted the nanostructures of Cu based oxides, hydroxides, sulfides, selenides, tellurides and phosphides as catalysts for water splitting application and the merits of which have been explored in detail as a review. The possibilities of enhancing the activity and durability with Cu based catalysts were studied and among which enhancing the activity with the formation of nanostructures, growing over 3D conducting supports, enhancing the electrical conductivity with graphene, increasing the metallic active sites by different methods like electrodeposition, adding other transition metals and also by varying the stoichiometric ratios had resulted in ensuring astonishing activity and stability.

Figure 1. Cu nanostructures as catalysts for enabling high scale OER and HER activities by studying them as oxides, LDHs, chalcogenides and phosphides.

Authors:

K. Karthick

CSIR – Central Electrochemical Research Institute

K. Karthick had received his B.Sc degree from Government Arts and Science College, Udumalapet, India and M.Sc degree from The American College – Madurai, India in general chemistry. He qualified UGC-JRF in December-2014 and joined under Dr. Subrata Kundu’s research Group since August-2015. He is currently working towards his Ph.D thesis mainly focused on Electrocatalytic Water splitting applications.

https://scholar.google.co.in/citations?user=RU1m2ScAAAAJ&hl=en

Dr. Subrata Kundu

CSIR – Central Electrochemical Research Institute

Dr. Subrata Kundu received his Ph.D from the Indian Institute of Technology (IIT), Kharagpur, India in early 2005. Then he moved to University of Nebraska, Lincoln, USA and later to Texas A&M University, College station, Texas, USA as a post-doc fellow (from 2005 to 2010). He is currently working as a Senior Scientist at CSIR-CECRI, Karaikudi, India. Dr. Kundu is serving as an editorial board member of several international journals including prestigious ‘Scientific Reports’ from Nature publishers since 2015. Dr. Kundu and his co-workers are working in the forefront area of Material Sciences with emphasizes on energy, environment, catalysis and electrocatalysis.

https://scholar.google.co.in/citations?user=4siGGnQAAAAJ&hl=en

https://www.cecri.res.in/Profile?empcode=40257

https://anantharaj1402.wixsite.com/dr-sk-group

Article information:

Investigation on Nanostructured Cu Based Electrocatalysts for Improvising Water Splitting: A Review
Karthick Kannimuthu, K. Sangeetha, S. Sam Sankar, Arun Karmakar, Ragunath Madhu and Subrata Kundu
Inorg. Chem. Front., 2020, Accepted Manuscript
https://doi.org/10.1039/D0QI01060J

Arylamines are an important molecular unity that is widely used in the design and creation of organic functional materials for applications such as solar cells, light emitting diodes, and electrochromic devices. Due to their electron-rich nature, these molecules can be readily oxidized into radical cations, whose persistence is essential for the performance of organic electronic devices.

The properties of arylamines and their oxidized radical cation states can be modulated by coordination with transition metals at the nitrogen site, because of the inductive effect from the metal, and the interactions between the p-orbital on the nitrogen atom and the d orbitals of the metal center.

In the past few years, the Ozerov group and collaborators at Texas A&M University demonstrated synthesis and redox properties of several bimetallic pincer complexes with arylamine backbones, where two pincer-type metal cores were connected by non-conjugated linkers or ynediyl linkers via metal-ligand bonds. Recently, in collaboration with the Fang group at Texas A&M, they reported the synthesis of bimetallic complexes where two redox sites are connected with via organic ligand-to-ligand linkers that modulate the degree of separation between redox sites (Figure 1).

Figure 1. Bimetallic bis(pincer) complexes synthesized in this work.

Cyclic voltammograms of all these complexes revealed two quasireversible oxidation waves. For 1-3, the separation of the two oxidation waves increased as the proximity between two redox sites increased. The comproportionation constants were calculated, which revealed that compounds 2, 3, and 4 belong to the Robin-Day Class III mixed valence systems, whereas compound 1 falls into the range of Class II. The largest comproportionation constant of 3.1×10¹¹ was found in compound 3, suggesting the high stability of this radical cationic intermediate. UV-vis-NIR spectra of the radical cations of 2, 3, and 4 showed intensive absorption peaks in the NIR region, revealing the highly delocalized nature of these radical species. The Hush electron coupling integrals of these mixed valence molecules fall into the range of Class III systems, which is in a good agreement of the cyclic voltammetry analysis.

Figure 2. Cyclic voltammograms of complexes 1–4 (ca. 0.001 M in CH₂Cl₂) with [ⁿBu₄N]PF₆ electrolyte (0.1 M), scan rate 100 mV/s, potentials referenced to Fc⁺/Fc at 0 V.

Single-crystal diffraction was performed to establish solid-state structures of compounds 3, as well as its oxidized states, to shed the light on the mechanism of its oxidation process. The geometric differences among these structures lie mainly in the changes in the bond distances associated with the central p-diaminobenzene unit, which revealed the transformation from a benzenoidal structure to a quinoidal structure (Figure 3).

Figure 3. Dominant resonance forms of compound 3 at different oxidation states.

In conclusion, the square-planar palladium center imposes a more rigid geometry on the organic ligand that leads to different degrees of the pi delocalization over the extended system. A stronger electronic communication between two redox sites was found at a closer proximity between them. Such a presence of palladium centers is important in stabilizing the mono- and bis-oxidized forms of these molecules. These bis(pincer) complexes are potential building blocks for more complicated conjugated molecules and polymers that can find applications in organic electronic devices.

Authors:

Oleg V. Ozerov

Oleg Ozerov is Emile and Marta Schweikert Professor in the Department of Chemistry at Texas A&M University.  He received his Diploma (1998) from the Higher Chemical College of the Russian Academy of Sciences and his PhD degree (2000) from the University of Kentucky where he worked with Prof. Folami T. Ladipo.  Following a postdoctoral appointment with Prof. Kenneth G. Caulton in Indiana University (2000-02), Dr. Ozerov started his independent academic career at Brandeis University, before moving to Texas A&M in 2009.  He is a recipient of the ACS Award in Pure Chemistry (2012) and of the Norman Hackerman Award in Chemical Research from the Welch Foundation (2012), and has served as an associate editor of Inorganic Chemistry Frontiers since 2013.  The Ozerov group pursues studies in molecular transition metal and main group chemistry.

https://www.chem.tamu.edu/rgroup/ozerov/index.html

Lei Fang

Lei Fang is an associate professor in the Department of Chemistry at Texas A&M University. He received his BS (2003) and MS (2006) degrees from Wuhan University. His PhD study was started at University of California Los Angeles in 2006, and completed at Northwestern University in 2010, under the mentorship of Sir Fraser Stoddart. Subsequently, he spent two and a half years at Stanford University as a postdoctoral scholar working with Professor Zhenan Bao. In 2013, he joined the faculty of Texas A&M University, where he currently leads a multidisciplinary research team focusing on functional organic materials.

https://www.chem.tamu.edu/rgroup/fang/

Article information:

Palladium bis-pincer complexes with controlled rigidity and inter-metal distance
Cheng-Han Yu, Congzhi Zhu, Xiaozhou Ji, Wei Hu, Haomiao Xie, Nattamai Bhuvanesh, Lei Fang and Oleg V. Ozerov
Inorg. Chem. Front., 2020, Advance Article
https://doi.org/10.1039/D0QI01111H