مقاله انگلیسی رایگان در مورد ارزیابی قابلیت اطمینان از بازده تبدیل انرژی در DMFCs – الزویر 2018

Considering the effects of unpredictable disturbances, a robustness criterion is newly proposed to develop an integrated evaluation with modified efficiency criterion, for comprehensive assessments of energy conversion performances in direct methanol fuel cells. The effectiveness of developed criteria in various situations (including some extreme operating conditions) has been carefully analyzed based on both experimental and numerical results. For undisturbed operations, the modified efficiency criterion could help to avoid potential misinterpretations of energy conversion process in existing criteria. For disturbed operations, the robustness criterion concerning the effects of uncertainty propagations is shown to be an effective guidance for the determination of appropriate operating current densities to design efficiency-stabilized operations. Systematic analysis on its applications in different situations proves that, the integrated efficiency and robustness evaluations can effectively differentiate the effects of operating conditions and membrane types, which is highly beneficial for one’s optimal designs of stable and efficient DMFC operations.

Introduction

Direct Methanol Fuel Cell (DMFC) is regarded as a prosperous power source for mobile applications attributing to its features of easy handling, rapid charge and high energy density, etc. [1,2]. Lots of efforts have been carried out to improve the DMFC performance for accelerating its commercialization during the past decades [3], such as the optimization of cell structure [4], the improvement of catalyst loading [5] and the amelioration of fuel delivery system [6]. In one’s evaluations of those performance-enhanced techniques, how to determine an effective criterion for DMFC operations can be an important problem and therefore deserves further discussions [7,8]. A widely applied assessment of DMFC performance is the relationship of current density (I) and voltage (V) or power density (P), i.e., I-V or I-P curves. Coming very naturally from their definitions, the polarization effects and the output characteristics of DMFC systems can be well depicted [9,10]. However, the I-V and I-P curves mainly concentrate on the system output, rather than the energy conversion process. Under different hypotheses, several criteria were proposed to assess the energy conversion efficiency during the past decade [11,12]. One of the main criteria considers the fact that the energy conversion efficiency is highly relevant with the fuel waste (i.e., methanol crossover effect). It utilized a single-parameter index, the effectiveness of fuel utilization (the ratio between the power-generated fuel amount and the overall fuel consumption), to measure the energy conversion efficiency [11,12]. However, the output characteristics has not been taken into account. Considering the polarization effect, a double-parameter index was proposed to evaluate the overall efficiency by multiplying the potential and Faraday/current efficiencies [13,14]. A very similar criterion was also deduced from the ratio between the output power density and the low heating value of overall fuel consumption [15]. Another type of criterion that was designed to concern about more systematical effects is the triple-parameter index, in which the total efficiency was considered by a product of several parameters accounting for fuel consumption, thermodynamic and voltaic efficiencies [16–18]. Such systematic considerations for global efficiency were also applied to evaluate the DMFC system only at its largest power output [19]. In spite of huge progress has been made, most of the existing criteria have been confined to evaluate DMFC systems with stable operating conditions.