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Designing catalysts for clean energy generation and chemical transformation

- Interface and surface engineering in nanomaterials:  Introducing and implementing interface-rich sites and surface defects during the synthesis of nanostructures (examples: transition metal oxides, alloys, hydroxides, sulfides & phosphides) to efficiently enhance the catalytic efficiency of the materials for the target reactions. 

Interface-site between metal-phosphides on Cu: Active for water dissociation. (Kumar et al. ACS Energy Lett. 2021) 

- Morphology and composition of nanomaterials:  Precise control over the compositions, size, and well-defined morphologies of the nanoparticles are necessary for the development of efficient catalysts with superior activity, stability, and selectivity for the desired reactions. 

Porous NiFe nanocubes for water oxidation. (Kumar et al. ACS Appl. Mater. Interfaces, 2017) 

- Single atom catalysts (SACs):  Single atom catalysts with atomically dispersed metals have emerged as a new class of heterogeneous catalysts, offering 100% atom utilization and exhibits excellent catalytic activity compared with their nanoparticles counterparts. Finding novel strategies and new synthesis routes to stabilize the single atoms on a suitable substrate and tuning their coordination environment to tailor the catalytic activities and selectivities for the target reactions with an atomic-level understanding are of prime importance. 

 Surface-strain strategy for stabilizing ultrahigh-loading of Rh single atoms sites. (Kumar et al. Energy Environ. Sci., 2021) 

Electrochemical water splitting into oxygen and hydrogen

Water splitting composed of two-half reactions: 2 e- hydrogen evolution reaction (HER) and 4 H+/e- oxygen evolution reaction (OER), typically requires higher overpotential over the thermodynamic cell voltage of 1.23 V vs Reversible hydrogen electrode for producing hydrogen and oxygen. Highly active electrocatalysts are required to increase the reaction rates and selectivity for both reactions.   

- Hydrogen evolution reaction (HER):  The HER (2H+  +  2e-  ---> H2) is the 2e- cathodic reaction in water splitting, necessary to produce clean hydrogen fuel. For higher efficacy of water electrolysis, hybrid electrocatalyst is needed to reduce the HER overpotential in both acidic and alkaline media. At present, platinum is the benchmarking catalyst for HER but its high cost limit its widespread application. Developing next-generation  HER catalyst with performance superior to Pt and understanding their surface structure and unique properties that dictate the  HER performance is the need of the hour.

Self-supported 2D NiCo-LDH on 1D Cu outperforms Pt for alkaline hydrogen generation. (Kumar et al. Chem. Sci., 2020) 

- Oxygen evolution reaction (OER):  The OER (2H2O ---->  O2 + 4H+ + 4e-) is the counter anodic reaction in water electrolysis which requires 4H+ and 4e- transfer per oxygen generation generally limits the efficiency for water electrolysis. To enhance the rate of OER, noble metal bases Ir/Ru-oxides are employed. Designing high-performance low-cost OER catalyst over Ir/Ru-oxides and understanding the fundamental relationship between the catalytic activity to the active surface is necessary to enhance the efficiency for full water splitting.

Ru single-atom stabilized on surface oxygen-rich bimetallic alloy for oxygen evolution. (Kumar et al. Energy Environ. Sci., 2020) 

Electrochemical carbon dioxide reduction to chemical fuels

Carbon dioxide reduction reaction (CO2RR):  Designing highly efficient electrocatalysts for electrochemical carbon dioxide reduction reaction (CO2RR) to value-added chemicals and fuels is urgently needed to combat the energy and environmental threats because of upward CO2 emission from human activities. Modulating the catalyst's morphology, composition, surface defects, and introducing interface-sites with fundamental understanding is the key for selective CO2 reduction to desired chemicals.  

Electrochemical nitrogen fixation to ammonia

Nitrogen reduction reaction (NRR): Electrochemical nitrogen reduction to ammonia (an activated nitrogen building block for the manufacture of modern fertilizers, plastics, fibers, explosives, etc) under ambient conditions is regarded as a promising alternative to the traditional Haber-Bosch process. Developing efficient NRR catalysts with high ammonia yield and Faradaic efficiency, understanding the mechanism of the reaction is challenging and is of prime importance.  

Ru single-atom on cobalt oxide for NRR. (Kumar et al. ACS Energy Lett., 2021) 

Electrochemical oxygen reduction for fuel cells

Oxygen reduction reaction (ORR): The electrochemical oxygen reduction reaction (ORR) is an important reaction in many energy conversion/storage technologies, such as fuel cells, and metal air-batteries. ORR is mainly carried out using benchmarking Pt-based catalysts. Developing low-cost and efficient ORR catalysts will be a major step towards energy conversion/storage technologies and to combat the urgent environmental threats. 

Electrochemical 2-electron water oxidation to hydrogen peroxide 

Hydrogen peroxide (H2O2) electrosynthesis: Oxidizing water molecules (2 e- water oxidation) to value-added H2O2 at anode while simultaneously producing green hydrogen at the cathode is of great importance for sustainable and economical energy conversion process. Precisely tuning the active sites of electrocatalysts (eg. single atomic sites on metal oxides) can increase the selectivity/faradaic efficiency for H2O2 generation over molecular oxygen.   

Electrochemical organic transformation and small molecules oxidation  

- Electro-organic synthesis: Electrons supplied from renewable energies are applied for oxidation or reduction of organic compounds instead of expensive reagents, thereby avoiding reagent waste leading to high atom economy and outstanding sustainability. However, achieving excellent selectivity and reactivity under challenging reaction conditions remains an unsolved issue. Designing novel electrode materials based on single atom or single atom ensemble catalysts along with appropriate cell design are the key to success.    

- Electrooxidation of small molecules: Replacing the sluggish anodic oxygen evolution reaction with the thermodynamically favorable small molecules oxidation (urea, alcohols, hydrazine, amine, aldehyde, carbohydrates, etc) offers great promise for energy-saving hydrogen generation, additionally generating high-value chemicals or pollutant degradation at the anode. Development of efficient electrocatalysts to overcome the  intrinsically slow reaction kinetics of such anodic reactions is the need of the hour.

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