### 1. Introduction

_{4})xH

_{3}-xPO

_{4}), adsorption by molecular sieve or activated carbon [20], and formation of complexes with metal halides [21]. At present, higher purity hydrogen can be obtained by pressure swing adsorption, composite metal palladium membrane separation and other methods [22,23]. But for small portable PEMFC devices, these methods may seem too bulky. Therefore, the development of a PEMFC that directly utilizes ammonia decomposition gas (Referred as gas mixture in this paper) is of great interest and can greatly expand the application of PEMFC. The feasibility of ammonia as a fuel has been initially verified on a 100 W dead-ended PEMFC system by Hazel M.A. Hunter et al. [24].

### 2. Experimental

### 2.1. System description

_{2}O

_{3}catalyst, NiO>14wt.%), ammonia purifier (Plexiglas tube, diameter 100 mm, length 600 mm, filled with saturated salt water), gas dehumidifier, mass spectrometer. The working process of the system is as follows.

### 2.2 Experimental scheme

### 3. Mathematical modeling

Each gas is regarded as an ideal gas.

The generated water can quickly flow out with air in a gaseous form, and there is no liquid water in the cathode.

The temperature distribution in PEMFC is uniform and constant.

The penetration of water and nitrogen from the cathode side to the anode side is ignored.

### 3.1. Electrochemical model

*E*

*is the theoretical reversible voltage which can be calculated from the Nernst equation[ 22]:*

_{0}*i*

*(Butler-Volmer equation)*

_{a}*i*

*(Butler-Volmer equation)*

_{c}*F*is the Faraday’s constant (SI unit: C mol

^{−1}),

*c*

*is the material reference concentration (SI unit: mol m*

_{i,ref}^{−3}),

*i*

*and*

_{0,a}*i*

*is the standard exchange current density (SI unit: A m*

_{0,c}^{−2}),

*R*is the gas constant,

*T*is the temperature (SI unit: K),

*α*

*,*

_{a,a}*α*

*,*

_{a,c}*α*

*,*

_{c,a}*α*

*is the transfer coefficient.*

_{c,c}*η*

*, cathode over-potential*

_{a}*η*

*and total over-potential*

_{c}*η*

*are given by the following equation:*

_{act}*E*

*(SI unit: V) represents the equilibrium voltage,*

_{eq,i}*ϕ*

*is the electronic potential (IS unit: V), and*

_{s}*ϕ*

*is the ionic potential (IS unit: V).*

_{l}*η*

*:*

_{ohm}*σ*

*(IS unit: S m*

_{e}^{−1}) is the electrical conductivity (where the index

*e*stands for “a”(anode) or “c”(cathode)).

### 3.2. Momentum conservation equation

*ρ*is the mixture density of the gas phase (SI unit: kg m

^{−3}),

*I*is Unit Matrix,

*P*is the pressure (SI unit: Pa),

*μ*represents the gas viscosity (SI unit: Pa s), u is the velocity.

*k*is permeability(IS unit: m

^{2}),

*ɛ*is porosity.

### 3.3. Mass conservation equation

_{2}and N

_{2}) and three at the cathode (O

_{2}, H

_{2}O and N

_{2}), and uses Maxwell-Stefan multicomponent diffusion, governed by the following equations [29]:

*w*

*is mass fraction of species i,*

_{i}*R*

*is chemical reaction rate of species i(IS unit: kg m*

_{i}^{−3}s

^{−1}),

*j*

*is the diffusion mass flow density of species i, which is defined as follows:*

_{i}*x*

*is mole fraction,*

_{k}*M*

*is Molecular mass,*

_{i}*D*

*is binary diffusion coefficient, which can be calculated by Fuller’s empirical formula [30]:*

_{ik}*v*

*is the molar diffusion volume of gas (IS unit: cm*

_{i}^{3}mol

^{−1}).

*τ*is the tortuosity factor.