Review
Carbon capture, storage, and utilization
Nickel-nitrogen-carbon (Ni-N-C)
electrocatalysts toward CO2 electroreduction: Advances,
optimizations, challenges and prospects
Qingqing Pang, Xizheng Fan,
Kaihang Sun, Kun Xiang, Baojun Li, Shufang Zhao, Young Dok Kim, Qiaoyun
Liu,* Zhongyi Liu,* and Zhikun Peng*
((Optional Dedication))
Q. Pang, X. Fan, K. Sun, B. Li, Dr. Q. Liu, Prof. Z. Liu, Dr. Z. Peng
School of Chemical Engineering, College of Chemistry, Henan Institute of
Advance Technology, Zhengzhou University, Zhengzhou 450001, China
E-mail: liuqiaoyun@zzu.edu.cn; liuzhongyi@zzu.edu.cn;
pengzhikun@zzu.edu.cn
K. Xiang
School of Chemistry and Environmental Engineering
Wuhan Institute of Technology, Wuhan 430205, China
S. Zhao, Y. D. Kim
Department of Chemistry
Sungkyunkwan University, Suwon 16419, Republic of Korea
Keywords: Ni-N-C electrocatalysts, Active sites, Optimization
strategies, Electrocatalysis, CO2 reduction
Abstract: Electrocatalytic reduction of CO2 into high
energy-density fuels and value-added chemicals under mild conditions can
promote the sustainable cycle of carbon and decrease current energy and
environmental problems. Constructing electrocatalyst with high activity,
selectivity, stability and low cost is really matter to realize
industrial application of electrocatalytic CO2 reduction
(ECR). Metal-nitrogen-carbon (M-N-C) electrocatalysts, especially
Ni-N-C, display excellent performance, such as nearly 100% CO
selectivity, high current density, outstanding tolerance, etc., which is
considered to possess broad application prospects. Based on the current
research status, starting from the mechanism of ECR and the existence
form of Ni active species, the latest research progress of Ni-N-C
electrocatalysts in CO2electroreduction is systematically
summarized. An overview is emphatically interpreted on the regulatory
strategies for activity optimization over Ni-N-C, including N
coordination modulation, vacancy defects construction, morphology
design, surface modification, heteroatom activation, bimetallic
cooperation. Finally, some urgent problems and future prospects on
designing Ni-N-C catalyst for ECR are discussed. This review aims to
provide the guidance for the design and development of Ni-N-C catalyst
with practical application.
1. Introduction
Excess emission of greenhouse gas CO2 from massive
exploitation of fossil fuels, breaks the carbon cycle system in nature,
causing the global warming and biodiversity
reduction.[1-3]How to reduce CO2 emissions and turn them into reusable
fuels or chemicals has become one of the most urgent tasks. A great deal
of effort has been devoted to finding effective solutions to achieve the
important task of converting
CO2.[4-6] Compared with the
thermal and photocatalytic conversion of CO2, the
electrocatalytic CO2 reduction (ECR) technology with
mild conditions, controllability, environmental friendliness and high
efficiency is getting more and more
attention.[7-9] Overcoming the obstacles such as
desirable catalysts, steerable reaction conditions and devices, is
extremely crucial for realizing the maximum application value of ECR
technology. At present, although the ECR reaction achieved a variety of
gaseous and liquid products including formic acid (HCOOH), carbon
monoxide (CO), hydrocarbons (CH4 and
C2H4) and alcohols
(CH3OH and
C2H5OH),[10-14]the development of electrocatalysts with high selectivity and stability
to overcome slow kinetics and high overpotential is still the core
content for ECR.
In recent years, diverse electrocatalysts have been tried and employed
in ECR reaction, including precious metals,[15-17]transition metals[18-22] and metal-free
catalysts[23-25]. Among them, transition
metal-nitrogen-carbon (M-N-C) materials are considered to have great
potential as ECR electrocatalysts. On the one hand, nitrogen-doped
carbon as the substrate can anchor metal atoms or particles to enrich
the active sites and accelerate the electron transport rate; On the
other hand, the charge distribution and electronic structure of active
species can be regulated by the morphology design, defect construction
and heteroatom doping of the nitrogen-doped carbon matrix, achieving the
regulation of product type and selectivity.[26,27]Notably, Ni-coupled N-doped carbon
(Ni-N-C) catalyst has demonstrated
to possess more advantages than other transition metals including
current density, CO selectivity and stability, which is the hot topic in
ECR
field.[28-31]For instance, Yang et al. reported an extended multi-step pyrolysis
process for the preparation of monatomic nitrogen-doped carbon nanotubes
catalysts with high metal loads. The activity evaluation of nitrocarbon
catalyst for multifarious metals (MSA-N-CNTs, where M = Ni, Co, NiCo,
CoFe and NiPt) showed that NSA-N-CNTs exported the highest ECR activity,
and the CO selectivity was up to 91.3% at −0.7
V.[32] Furthermore, Hao et al. studied the
intrinsic catalytic activity, CO turnover and CO Faraday efficiency of
M-N-C (M = Mn, Fe, CO, Ni, Cu)
electrocatalysts containing the active species
M-Nx . It was confirmed that
Ni-Nx single site exhibited unique reactivity and
Faraday efficiency in the reduction process from CO2 to
CO, which produced the most CO at high potential. The above findings
illustrate the great potential of Ni-N-C materials in ECR, including
excellent electrical conductivity and stability, high current density,
and near 100% CO selectivity, meeting and even exceeding the mass
activity of advanced precious metal
catalysts.[33,34] Based on the extraordinary
potential of Ni-N-C catalysts in the ECR field, the relatively
systematic summary is essential.
Combining the experimental and theoretical investigations of Ni-N-C, we
systematically summarized the recent progress of Ni-N-C electrocatalyst
in the field of CO2 electroreduction technology. On
account of the mechanism of CO2 electrocatalytic
reduction, the construction strategy, systematic classification,
activity regulation and product selectivity of advanced Ni-N-C
electrocatalysts were systematically reviewed. The structure-activity
relationship of Ni-N-C electrocatalyst was emphasized by surface
modification, defect engineering, change of coordination environment
over active sites and reactor optimization. At the end of the paper, the
challenges and future prospects are presented. Through this review, we
anticipate providing new insights that can benefit for enhancing ECR.
Our work may provide the basis and strategies for program upgrading in
terms of improving the efficiency of electrocatalytic reduction over
CO2 and achieving industrialization.