Prasad Prakash Patel

Noble metal-free bifunctional oxygen evolution and oxygen reduction acidic media electro-catalysts

Identification of low cost, highly active, durable completely noble metal-free electro-catalyst for oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells, oxygen evolution reaction (OER) in PEM based water electrolysis and metal air batteries remains one of the major unfulfilled scientific and technological challenges of PEM based acid mediated electro-catalysts. In contrast, several non-noble metals based electro-catalysts have been identified for alkaline and neutral medium water electrolysis and fuel cells. Herein we report for the very first time, F doped Cu1.5Mn1.5O4, identified by exploiting theoretical first principles calculations for ORR and OER in PEM based systems. The identified novel noble metal-free electro-catalyst showed similar onset potential (1.43 V for OER and 1 V for ORR vs RHE) to that of IrO2 and Pt/C, respectively. The system also displayed excellent electrochemical activity comparable to IrO2 for OER and Pt/C for ORR, respectively, along with remarkable long term stability for 6000 cycles in acidic media validating theory, while also displaying superior methanol tolerance and yielding recommended power densities in full cell configurations.

Nanostructured robust cobalt metal alloy based anode electro-catalysts exhibiting remarkably high performance and durability for proton exchange membrane fuel cells

In recent years, the development of durable and electrochemically active electro-catalyst alloys with reduced noble metal content exhibiting similar or better electrochemical performance than pure noble metal electro-catalysts has gathered considerable momentum particularly, for proton exchange membrane fuel cell (PEMFC) application. Engineering such reduced noble metal containing electro-catalyst alloys in nano-scale dimensions with highly active electrochemical surface area (ECSA) will ultimately translate to reduced noble metal loadings to ultra-low levels which will eventually lead to an overall reduction in the capital cost of PEMFCs. Herein we report the development of nanostructured Co–Ir based solid-solution electro-catalyst alloys for the hydrogen oxidation reaction (HOR) further validated by first principles theoretical calculation of the d band center of the transition metal in the solid solution alloys. The theoretical and experimental studies reported herein demonstrate that the nanostructured alloy electro-catalysts comprising 70 at% Co (Co0.7Ir0.3) and 60 at% Co (Co0.6Ir0.4) of crystallite size ∼4 nm with a high electrochemically active surface area (ECSA) (∼56 m2 g−1) exhibit improved electrochemical activity (reduction in overpotential and improved reaction kinetics) for the HOR combined with outstanding durability in contrast to pure Ir nanoparticles (Ir-NPs) as well as state of the art commercial Pt/C system. Moreover, an optimized alloy containing 60 at% Co (Co0.6Ir0.4) showed a remarkable ∼156% and 92% higher electro-catalytic activity for the HOR than Ir-NPs and commercial 40% Pt/C, respectively, with similar loading and ECSA. The single PEMFC full cell study also shows ∼85% improved maximum power density for the Co0.6(Ir0.4) electro-catalyst compared to 40% Pt/C and excellent electrochemical stability/durability comparable to 40% Pt/C.

WO3 based solid solution oxide – promising proton exchange membrane fuel cell anode electro-catalyst

There is a vital need to develop novel non-noble metals based electro-catalyst or reduced noble metal containing electro-catalyst with excellent electrochemical activity and stability fostering economic commercialization of proton exchange membrane fuel cells (PEMFCs). It is hence of paramount importance to identify and generate reduced noble metal containing electro-catalyst with high electrochemical active surface area, offering noble metal loadings in the ultra-low levels thus reducing the overall capital cost of PEMFCs. Using theoretical first principles d-band center calculations of tungsten trioxide (WO3) based electro-catalysts containing IrO2 as a solute for hydrogen oxidation reaction (HOR), we have identified, synthesized and experimentally demonstrated a highly active nanostructured (W1−xIrx)Oy (x = 0.2, 0.3; y = 2.7–2.8) electro-catalyst for HOR. Furthermore, experimental studies validate superior electrochemical activity of nanostructured (W0.7Ir0.3)Oy for HOR exhibiting improved/comparable stability/durability contrasted to pure WO3 nanoparticles (WO3-NPs), IrO2 nanoparticles (IrO2-NPs) as well as state of the art commercial 40% Pt/C system. Optimized composition of (W0.7Ir0.3)Oy was identified exhibiting ∼33% higher and almost similar electro-catalytic activity for HOR compared to IrO2-NPs and commercial 40% Pt/C catalyst, respectively. Additionally, (W0.7Ir0.3)Oy showed significant enhancement in electrochemical activity for HOR compared to pure WO3-NPs. Long-term life cycle test of (W0.7Ir0.3)Oy for 24 h also showed comparable electrochemical stability/durability compared to that of 40% Pt/C and pure WO3-NPs. The results of half and full cell electrochemical characterization bode well with the theoretical first principles studies demonstrating the promise of the WO3 based solid solution electro-catalyst.

Fluorine substituted (Mn,Ir)O2:F high performance solid solution oxygen evolution reaction electro-catalysts for PEM water electrolysis

Identification and development of high performance with reduced overpotential (i.e. reduced operating electricity cost) oxygen evolution reaction (OER) electrocatalysts for proton exchange membrane (PEM) based water electrolysis with ultra-low noble metal content (i.e. reduced materials cost) is of significant interest for economic hydrogen production, thus increasing the commercialization potential of PEM water electrolysis. Accordingly, a novel electrocatalyst should exhibit low overpotential, excellent electrochemical activity and durability superior to state of the art noble metal based electro-catalysts (e.g. Pt, IrO2, RuO2). Herein, for the very first time to the best of our knowledge, exploiting first-principles theoretical calculations of the total energies and electronic structures, we have identified a reduced noble metal content fluorine doped solid solution of MnO2 and IrO2, denoted as (Mn1−xIrx)O2:F (x = 0.2, 0.3, 0.4), OER electrocatalyst system exhibiting lower overpotential and higher current density than the state of the art IrO2 and other previously reported systems for PEM water electrolysis. The doped solid solution displays an excellent electrochemical performance with a lowest reported onset potential to date of ∼1.35 V (vs. RHE), ∼80 mV lower than that of IrO2 (∼1.43 V vs. RHE) and ∼15 fold (x = 0.3 and 0.4) higher electrochemical activity compared to pure IrO2. In addition, the system displays excellent long term electrochemical durability, similar to that of IrO2 in harsh acidic OER operating conditions. Our study therefore demonstrates remarkable, ∼60–80% reduction in noble metal content along with lower overpotential and excellent electrochemical performance clearly demonstrating the potential of the (Mn1−xIrx)O2:F system as an OER electro-catalyst for PEM water electrolysis.

A rapid solid-state synthesis of electrochemically active Chevrel phases (Mo6T8; T = S, Se) for rechargeable magnesium batteries

High energy mechanical milling (HEMM) of a stoichiometric mixture of molybdenum and metal chalcogenides (CuT and MoT2; T = S, Se) followed by heat treatment at elevated temperatures was successfully applied to synthesize Chevrel phases (Cu2Mo6T8; T = S, Se) as positive electrodes for rechargeable magnesium batteries. Differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to understand the phase formation following milling and heat treatment. CuS and Mo were observed to react at 714–800 K and formed an intermediate ternary Chevrel phase (Cu1.83Mo3S4), which further reacted with residual Mo and MoS2 to form the desired Cu2Mo6S8. Quantitative XRD analysis shows the formation of a ∼96%–98% Chevrel phase at 30 min following the milling and heat treatment. The electrochemical performance of de-cuprated Mo6S8 and Mo6Se8 phases were evaluated by cyclic voltammetry (CV), galvanostatic cycling, and electrochemical impedance spectroscopy (EIS). The results of the CV and galvanostatic cycling data showed the expected anodic/cathodic behavior and a stable capacity after the first cycle with the formation of MgxMo6T8 (T = S, Se; 1 ≤ x ≤ 2). EIS at ∼0.1 V intervals for the Mo6S8 electrode during the first and second cycle shows that partial Mg-ion trapping resulted in an increase in charge transfer resistance Re. In contrast, the interfacial resistance Ri remained constant, and no significant trapping was evident during the galvanostatic cycling of the Mo6Se8 electrode. Importantly, the ease of preparation, stable capacity, high Coulombic efficiency, and excellent rate capabilities render HEMM a viable route to laboratory-scale production of Chevrel phases for use as positive electrodes for rechargeable magnesium batteries.