Challenges are faced for
rapid economic and social development including the global energy shortage,
diversification in energy and chemical raw materials, and ecological
environmental protection. The development of renewable energy has become a
common concern for the current society. Energy relevant-catalysis reaction is
the core of energy conversion and chemical processes, aiming to achieve high
energy power sources, conversion of reaction feedstocks, and selectivity of
target products under mild conditions. More than 85% of energy and chemical
processes are closely related to catalysis reaction, that is, driven by highly
effective catalysts. It is significant to establish the structural performance
relationship by deciphering the atomic structure and electronic states of
active sites, which provides new sights into the catalytic processes and
promotes the development of novel catalyst materials. Therefore, as supported
by Chinese Journal of Structural Chemistry, a special issue for the Structural
Chemistry in Energy Relevant-Catalysis Reaction was organized by the Guest
Editors.
Rational
design of Fe and N co-doped carbon catalysts (Fe-NCs), one promising
non-precious cathode catalyst, is critical to commercialization of proton
exchange membrane fuel cells. The atomic Fe site density of Fe-NCs is critical
to improve catalytic currents approaching industrial levels. One recent
research proposes a template-guided strategy to break the limit of Fe site
density, and greatly promotes the fuel cell performance.
With
the increasing demand for energy, various emerging energy storage/conversion
technologies have gradually penetrated human life, providing numerous
conveniences. The practical application efficiency is often affected by the
slow kinetics of hydrogen or oxygen electrocatalytic reactions (hydrogen
evolution and oxidation reactions, oxygen evolution and reduction reactions)
among the emerging devices. Therefore, the researchers devote to finding
cost-effective electrocatalysts. Non-noble metal catalysts have low cost and
good catalytic activity, but poor stability, agglomeration, dissolution, and
other problems will occur after a long cycle, such as transition metal oxides
and carbides. Transition metal nitrides (TMNs) stand out among all kinds of
non-noble metal catalysts because of the intrinsic platinum-like
electrocatalytic activities, relatively high conductivity, and wide range of
tunability. In this review, the applications of TMNs in
electrocatalytic fields are summarized based on the number of metals contained
in TMNs. The practical application potentials of TMNs in fuel cell, water
splitting, zinc-air battery and other electrochemical energy storage/conversion
devices are also listed. Finally, the design strategies and viewpoints of
TMNs-based electrocatalyst are summarized. The potential challenges of
TMNs-based electrocatalyst in the development of electrocatalytic energy
devices in the future are prospected.
Platinum-Ruthenium (PtRu)-based materials are considered the “holy
grail” of electrocatalysts for methanol oxidation reaction (MOR) in the fuel
cells technique. However, to the best of our knowledge,
the exhaustive review report on the advance of PtRu materials for methanol
oxidation is rarely summarized for the recent novel achievements. Herein,
we summarize and discuss the latest progress of PtRu-based catalysts in MOR.
The reaction mechanism of MOR is firstly introduced, and the promotion
mechanism is revealed by the relevant activity descriptor, the in-situ
spectroscopic analysis and the theoretical calculation. Subsequently, some
advanced regulation strategies of PtRu-based catalysts are concluded, including
support engineering, morphology design and surface interface regulation.
Finally, the challenges and opportunities to improve the MOR performance of
PtRu-based electrocatalysts are prospected to further promote the widespread
application of PtRu-based catalysts in electrocatalytic systems. It is
concluded that many efforts are still required to decipher the atomic scale
structure-activity relationship and the structural changes of atoms and
electrons in the reaction process by advanced strategies and characterization
methods. Hopefully, this review can be helpful for novel PtRu-based catalyst
development and understanding their correlation to the structure and
performance of energy-relevant electrocatalysis.
Nickel (Ni)-based materials are promising electrocatalysts for the urea
electrooxidation reaction, as the in situ formed NiOOH species on their surface during operation are catalytically active
sites. In this work, phytate-coordinated Ni foam (PA-NF) is shown to deliver a
high catalytic performance toward the urea electrooxidation reaction, with a low
potential of 1.38 V at 10 mA/cm2, a low Tafel slope of 64.1 mV/dec,
and superior catalytic stability; a performance comparable to state-of-the-art Ni-based catalysts. Electrochemical
characterization alongside the control experiments revealed that such a high performance could be
ascribed to kinetically-accelerated surface reconstruction and the enrichment
of NiOOH active species on the PA-NF surface during the electrooxidation of urea
owing to PA-coordination induced upshift of d-band center of Ni sites. Overall, a new strategy is provided for the
design of an efficient and universal Ni-based catalyst for the electrooxidation
of urea, which can also be extended to other transition-metal-based systems.
Developing
efficient and durable electrocatalysts for water splitting, which has long been
regarded as one of the most promising patterns to produce green hydrogen, is of
great significance but still challenging. Herein, ample Co/MoN heterogeneous
domains/nitrogen-doped carbon (Co/MoN/NC) nanosheet arrays as high-performance
hydrogen evolution reaction (HER) electrocatalyst via a typical
nitriding-carbonization strategy are successfully prepared on nickel foam (NF),
which exhibits a low overpotential of 29 mV at 10 mA cm-2, together
with excellent durability at 20 mA cm-2 for 90 h in alkaline
solution. Such excellent catalytic property for HER can be attributed to the
generation of abundant Co/MoN heterogeneous structures. Additionally, the high
conductivity of Co/MoN and NC also increases the charge transfer rate, further
helping accelerate the reaction rate of HER. This work presents an efficient
method for improving the catalytic hydrogen evolution activity in basic
solution.
The
porphyrin-based MOFs formed by combining Zr6 clusters and porphyrin
carboxylic acids with clear M-N4 active centers show unique
advantages in electrocatalytic reduction of CO2 (CO2RR).
However, its conductivity is still the bottleneck that limits its catalytic
activity due to the electrical insulation of the Zr cluster. Therefore, the porphyrin-based MOFs of PCN-222(M) (M = Mn, Co, Ni, Zn) with
explicit M-N4 coordination were combined with the highly conductive
material carbon nanotube (CNT) for discussing the influence of metal centers on
the CO2RR performance based on
theoretical calculations and experimental observations. The results show that
the PCN-222(Mn)/CNT, PCN-222(Co)/CNT, and
PCN-222(Zn)/CNT all exhibit high selectivity to CO (FECO > 80%) in
the range of -0.60 to -0.70 V vs. RHE. The FECOmax of
PCN-222(Mn)/CNT (-0.60 V vs. RHE), PCN-222(Co)/CNT (-0.65 V vs. RHE), and
PCN-222(Zn)/CNT (-0.70 V vs. RHE) are 88.5%, 89.3% and 92.5%, respectively. The
high catalytic activity of PCN-222(Mn)/CNT and PCN-222(Co)/CNT comes from the
excellent electron mobility of their porphyrin rings and their low ΔG*COOH (0.87 and 0.58 eV). It reveals that the strength of backbonding π of the transition metal and its influence on the
electron mobility in the porphyrin ring can affect its CO2RR
activity.
The
heterojunction interfacial modulation of FeP is an effective strategy to
regulate the intrinsic activity and stability, which is a major challenge to
promote the industrial application of FeP-based electrocatalysts. Herein,
hollow Fe4C/FeP box with heterojunction interface and carbon armor
is successfully synthesized, which can expose numerous active sites and protect
catalyst from corrosion. Electrochemical measurements show that Fe4C/FeP
exhibits excellent hydrogen evolution activity and stability. It only needs 180
mV to achieve the current density of 10 mA cm-2. The high-activity
may be due to the synergistic effects of porous framework, graphitic carbon
coating and heterojunction structure of Fe4C
and FeP, which optimize the electronic structure and accelerates electron
transfer. In addition, the target catalyst can withstand 5000 cycles of CV
testing without significant change in properties. The
excellent stability may be attributed to the graphitic carbon coating as the
armor that can prevent the catalyst from corrosion of electrolyte. This
work may provide a synthetic approach to produce a series of carbon-coated and
heterojunction structure of transition metal phosphides for water splitting.
Insufficient
activity and instability (poisoning) of Pt-based electrocatalysts for
methanol oxidation and oxygen reduction reactions (MOR/ORR) impede the
development of direct methanol
fuel cells. Here, CoWO4 nanoparticles-loaded WO3 microrods coated by a thin carbon-layer are used as Pt-supports/co-catalysts
for MOR/ORR. WO3 grows along the (110) crystal plane to form
microrod (diameter of ~0.6 um),
which is coated by a carbon-layer (~5 nm). Pt-CoWO4/WO3@NCL-mr (850 ℃) shows a higher mass activity (2208 mA mg-1pt)
than the commercial Pt/C
(659.4 mA mg-1pt). CoWO4/WO3 heterojunction on the microrod surface
with abundant oxygen vacancies allows the generation of surface-adsorbed
hydroxyl to facilitate CO elimination and regeneration of the occupied Pt
active-sites (promising stability). Pt-CoWO4/WO3@NCL-mr
(850 ℃) has higher half-wave (0.46 V) and onset (0.54 V)
potentials than Pt/C (0.41 and 0.50 V) for ORR. The microrod structure of CoWO4/WO3@NCL facilitates the dispersibility of Pt NPs to
increase the utilization of Pt active sites and relieve the self-aggregation of
Pt to obtain a promising synergy between Pt and CoWO4 (Co2+) for ORR in acid media. This
study provides insights not only into the synthesis of acid-resistant WO3@NCL
microrod as active Pt co-catalyst, but also into the effective
utilization of surface oxygen
vacancies and Co2+ for MOR/ORR.
Rational
design of highly efficient and durable electrocatalysts with low cost to
replace noble-metal based catalysts for seawater electrolysis is extremely
desirable, but challenging. In this work, we demonstrate a rapid
electrodeposition method by growing P-Ni4Mo on the surface of the
copper foam (CF) substrate to synthesize an efficient seawater electrolysis
catalyst (P-Ni4Mo/CF). The catalyst exhibited considerable HER
performance and stability in alkaline seawater, with the overpotential as low
as 260 mV at a current density of 100 mA cm-2. The P-Ni4Mo/CF is capable of achieving 1.0 A cm-2 with an overpotential of 551 mV, which is slightly worse than that of
the Pt/C catalyst (453 mV). Moreover, P-Ni4Mo/CF demonstrates robust
durability, with almost no activity loss after the durability test for more
than 200 h. This work not only reports a new catalyst for seawater
electrolysis, but also presents a strategy for the performance enhancement of
seawater electrolysis.
Developing highly
efficient, easy-to-make and cost-effective bifunctional electrocatalysts for
water splitting with lower cell voltages is crucial to producing massive
hydrogen fuel. In response, the coupled hierarchical Ni/Fe-based MOF nanosheet
arrays with embedded metal sulfide nanoclusters onto nickel foam skeleton
(denoted as Fe-Ni3S2 @NiFe-MOF/NF) are fabricated, in
which the Fe-Ni3S2 clusters could
effectively restrain the aggregation of the layer
metal-organic frameworks (MOF) nanosheets and adjust the local electronic
structures of MOFs nanosheets. Benefiting from the rapid charge transfer and the
exposure of abundant active sites, the well-designed Fe-Ni3S2@NiFe-MOF/NF
displays excellent oxygen evolution reaction (OER) and hydrogen evolution
reaction (HER) performance. More importantly, when equipped in the alkaline
water electrolyzer, the Fe-Ni3S2@NiFe-MOF/NF enables the
system with a mere 1.6 V for achieving the current density of 10 mA cm-2.
This work offers a paradigm for designing efficient bifunctional HER/OER
electrocatalysts based on the hybrid materials of nanostructured metal sulfide
and MOF.