More Like this

1. Nickel selenide as an efficient electrocatalyst for selective reduction of carbon dioxide to carbon-rich products

   https://doi.org/10.1039/d2cy00583b  

   Saxena, Apurv ; Liyanage, Wipula P. ; Kapila, Shubhender ; Nath, Manashi ( August 2022 , Catalysis Science & Technology)

   Identifying new catalyst composition for carbon dioxide electroreduction to high-value products has been the center of attraction over the last several years. In this article, nickel selenide (NiSe 2 ) has been identified as a high-efficiency electrocatalyst for CO 2 electroreduction at neutral pH. Interestingly, NiSe 2 shows high selectivity towards specific reduction products, forming carbon-rich C2 products like ethanol and acetic acid exclusively at lower applied potential with 98.45% faradaic efficiency, while C1 products formic acid and carbon monoxide formed preferentially at higher applied potential. More importantly, the C2 products such as acetic acid and ethanol are obtained at very low applied potential, which further corroborates the novelty of this catalyst in CO 2 utilization with minimal energy expense. The NiSe 2 catalyst surface has been studied through density functional theory calculations which show that the adsorption energy of the CO intermediate on the NiSe 2 surface is optimal for extensive reduction through formation of C–C bonds but not strong enough for surface passivation, thus leading to high selectivity for C2 products. Such high efficiency of the catalyst can be a result of increased covalency of the selenide anion along with a high d-electron density of the Ni center.more »The hydrothermally synthesized NiSe 2 sample also shows high activity for oxygen evolution through electrocatalytic water splitting in alkaline medium, effectively making it a bifunctional catalyst which can lower the concentration of the atmospheric pollutant CO 2 while at the same time enriching the air with O 2 .« less
2. Planar defect-driven electrocatalysis of CO ₂ -to-C ₂ H ₄ conversion

   https://doi.org/10.1039/d1ta02565a  

   Li, Zhengyuan ; Fang, Yanbo ; Zhang, Jianfang ; Zhang, Tianyu ; Jimenez, Juan D. ; Senanayake, Sanjaya D. ; Shanov, Vesselin ; Yang, Shize ; Wu, Jingjie ( January 2021 , Journal of Materials Chemistry A)

   The selectivity towards a specific C 2+ product, such as ethylene (C 2 H 4 ), is sensitive to the surface structure of copper (Cu) catalysts in carbon dioxide (CO 2 ) electro-reduction. The fundamental understanding of such sensitivity can guide the development of advanced electrocatalysts, although it remains challenging at the atomic level. Here we demonstrated that planar defects, such as stacking faults, could drive the electrocatalysis of CO 2 -to-C 2 H 4 conversion with higher selectivity and productivity than Cu(100) facets in the intermediate potential region (−0.50 ∼ −0.65 V vs. RHE). The unique right bipyramidal Cu nanocrystals containing a combination of (100) facets and a set of parallel planar defects delivered 67% faradaic efficiency (FE) for C 2 H 4 and a partial current density of 217 mA cm −2 at −0.63 V vs. RHE. In contrast, Cu nanocubes with exclusive (100) facets exhibited only 46% FE for C 2 H 4 and a partial current density of 87 mA cm −2 at an identical potential. Both ex situ CO temperature-programmed desorption and in situ Raman spectroscopy analysis implied that the stronger *CO adsorption on planar defect sites facilitates CO generation kinetics, which contributes to amore »higher surface coverage of *CO and in turn an enhanced reaction rate of C–C coupling towards C 2+ products, especially C 2 H 4 .« less
3. Directing the reactivity of metal hydrides for selective CO ₂ reduction

   https://doi.org/10.1073/pnas.1811396115  

   Ceballos, Bianca M. ; Yang, Jenny Y. ( November 2018 , Proceedings of the National Academy of Sciences)

   A critical challenge in electrocatalytic CO₂reduction to renewable fuels is product selectivity. Desirable products of CO₂reduction require proton equivalents, but key catalytic intermediates can also be competent for direct proton reduction to H₂. Understanding how to manage divergent reaction pathways at these shared intermediates is essential to achieving high selectivity. Both proton reduction to hydrogen and CO₂reduction to formate generally proceed through a metal hydride intermediate. We apply thermodynamic relationships that describe the reactivity of metal hydrides with H⁺and CO₂to generate a thermodynamic product diagram, which outlines the free energy of product formation as a function of proton activity and hydricity (∆G_H−), or hydride donor strength. The diagram outlines a region of metal hydricity and proton activity in which CO₂reduction is favorable and H⁺reduction is suppressed. We apply our diagram to inform our selection of [Pt(dmpe)₂](PF₆)₂as a potential catalyst, because the corresponding hydride [HPt(dmpe)₂]⁺has the correct hydricity to access the region where selective CO₂reduction is possible. We validate our choice experimentally; [Pt(dmpe)₂](PF₆)₂is a highly selective electrocatalyst for CO₂reduction to formate (>90% Faradaic efficiency) at an overpotential of less than 100 mV in acetonitrile with no evidence of catalyst degradation after electrolysis. Our report of a selective catalyst for CO₂reduction illustratesmore »how our thermodynamic diagrams can guide selective and efficient catalyst discovery.

   « less
4. High-performance fuel cell cathodes exclusively containing atomically dispersed iron active sites

   https://doi.org/10.1039/C9EE00877B  

   Zhang, Hanguang ; Chung, Hoon T. ; Cullen, David A. ; Wagner, Stephan ; Kramm, Ulrike I. ; More, Karren L. ; Zelenay, Piotr ; Wu, Gang ( August 2019 , Energy & Environmental Science)

   Platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) with atomically dispersed FeN 4 sites have emerged as a potential replacement for low-PGM catalysts in acidic polymer electrolyte fuel cells (PEFCs). In this work, we carefully tuned the doped Fe content in zeolitic imidazolate framework (ZIF)-8 precursors and achieved complete atomic dispersion of FeN 4 sites, the sole Fe species in the catalyst based on Mößbauer spectroscopy data. The Fe–N–C catalyst with the highest density of active sites achieved respectable ORR activity in rotating disk electrode (RDE) testing with a half-wave potential ( E 1/2 ) of 0.88 ± 0.01 V vs. the reversible hydrogen electrode (RHE) in 0.5 M H 2 SO 4 electrolyte. The activity degradation was found to be more significant when holding the potential at 0.85 V relative to standard potential cycling (0.6–1.0 V) in O 2 saturated acid electrolyte. The post-mortem electron microscopy analysis provides insights into possible catalyst degradation mechanisms associated with Fe–N coordination cleavage and carbon corrosion. High ORR activity was confirmed in fuel cell testing, which also divulged the promising performance of the catalysts at practical PEFC voltages. We conclude that the key factor behind the high ORR activity ofmore »the Fe–N–C catalyst is the optimum Fe content in the ZIF-8 precursor. While too little Fe in the precursors results in an insufficient density of FeN 4 sites, too much Fe leads to the formation of clusters and an ensuing significant loss in catalytic activity due to the loss of atomically dispersed Fe to inactive clusters or even nanoparticles. Advanced electron microscopy was used to obtain insights into the clustering of Fe atoms as a function of the doped Fe content. The Fe content in the precursor also affects other key catalyst properties such as the particle size, porosity, nitrogen-doping level, and carbon microstructure. Thanks to using model catalysts exclusively containing FeN 4 sites, it was possible to directly correlate the ORR activity with the density of FeN 4 species in the catalyst.« less
5. The mechanism for acetate formation in electrochemical CO ₍₂₎ reduction on Cu: selectivity with potential, pH, and nanostructuring

   https://doi.org/10.1039/d2ee01485h  

   Heenen, Hendrik H. ; Shin, Haeun ; Kastlunger, Georg ; Overa, Sean ; Gauthier, Joseph A. ; Jiao, Feng ; Chan, Karen ( September 2022 , Energy & Environmental Science)

   Nanostructured Cu catalysts have increased the selectivities and geometric activities for high value C–C coupled (C 2 ) products (ethylene, ethanol, and acetate) in the electrochemical CO (2) reduction reaction (CO (2) RR). The selectivity among the high-value C 2 products is also altered, where for instance the yield of acetate increases with alkalinity and is dependent on the catalyst morphology. The reaction mechanisms behind the selectivity towards acetate vs. other C 2 products remain controversial. In this work, we elucidate the reaction mechanism for acetate formation by using ab initio simulations, a coupled kinetic-transport model, and loading dependent experiments. We find that trends in acetate selectivity can be rationalized from variations in electrolyte pH and the local mass transport properties of the catalyst and not from changes in Cu's intrinsic activity. The selectivity mechanism originates from the transport of ketene, a stable (closed shell) intermediate, away from the catalyst surface into solution where it reacts to form acetate. While this type of mechanism has not yet been discussed in the CO (2) RR, variants of it may explain similar selectivity fluctuations observed for other stable intermediates like CO and acetaldehyde. Our proposed mechanism suggests that acetate selectivity increases withmore »increasing pH, decreasing catalyst roughness and significantly varies with the applied potential.« less